Contrary to popular belief, Christianity and Catholicism are not the same religion. The popular belief that Catholicism is Christianity is damaging on several levels, first because it spreads heresy throughout the Church, and second because it gives unbelievers the wrong impression. I have often tried to witness to many unbelievers whose main objections to Christianity are actually objections to the Catholic Church.
It's surprising to me that so many people still believe Catholicism is Christianity, because it's actually very easy to refute. Why is this, you ask? It's so easy to refute because you only need two Bible verses and an understanding of the foundation of the Catholic faith. Since its inception, Catholicism has relied very heavily on what it calls "sacred tradition", which are supposed to be authoritative, equal to scripture. Some traditions are even supposed to be so authoritative that those who reject it are (or at the very least were until the late 1800s when Pope Leo XIII coined the term "separated brethren") anathema, i.e. damned to Hell. These traditions include, but are not limited to, the Catholic version of the Eucharist, the perpetual virginity of Mary and the Primacy of Peter. But the Bible has a very different story to tell. In just 2 verses, Paul gives Timothy the key to destroying the entire foundation of the Catholic Church. He says, in no uncertain terms, "All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work." (NKJV, emphasis mine).
During the Reformation, this concept became known as Sola Scriptura (Scripture Alone). It states that scripture, being the very word of God, plainly lays down all matters that concern faith and the manner of life. Extra-Biblical traditions may have some good in them (there is, for example, evidence that Jesus celebrated Hanukkah, which is not a Biblical tradition), but they are not authoritative. They are optional at best (Romans 14:1; Colossians 2:16-17), heretical at worst (Matthew 15:3; Mark 7:8-13; Colossians 2:8).
If Christianity is based solely on scripture, and not on tradition, whereas Catholicism is based mostly on tradition, even to the point of disobedience to scripture, it stands to reason that the two are different faiths. Realistically, you can stop there. There is nothing that can be said to rescue Catholicism at this point. Different foundation = different faith. But just because you can stop there doesn't mean you need to. It's all well and good showing that Catholicism relies too heavily on tradition to be Christianity, but it's even more powerful to show that many Catholic traditions are actually anti-Christian. In the rest of this article, I will examine a few examples.
Mariology
Like most Catholic doctrines, the Catholic view of Mary has evolved over the centuries, whereas the Christian view of Mary has remained static, having been recorded in the Bible for nearly 2,000 years. We don't know a huge amount about Mary, because she isn't mentioned much in the Bible. The Catholic Church, however, begs to differ. Within Catholicism are several dogmas, including her immaculate conception (i.e. she was conceived without original sin), her perpetual virginity (i.e. she remained a virgin for her entire life, even after Jesus was born and she married Joseph) and her assumption into Heaven (her body was taken to Heaven). Mary is also viewed (unofficially, for now) by many Catholics as co-redemtrix with Jesus, and several past Popes have claimed as much. How much of this is true? None.
First, was Mary conceived without original sin? As we have seen, if something isn't mentioned in the Bible, it is not Christian doctrine. There is one more verse we can add here: Amos 3:7 "Surely the Lord God does nothing, Unless He reveals His secret to His servants the prophets." (NKJV). What this means is that if God is going to interfere with the normal flow of reality, at least one prophet will know about it ahead of time. We see this with Jesus a lot. The Old Testament is flooded with prophecies and references to Jesus, including the circumstances of His birth. Isaiah 7:14 prophesied that He would be born of a virgin, He was born of a virgin. Micah 5:2 says He would be born in Bethlehem, He was born in Bethlehem. I could go on, but that's for another day. The point is, being conceived without original sin is not a regular occurrence, and so according to Amos 3:7, God would have told a prophet before it happened. Yet, no prophet, nor any passage of scripture, even hints at the idea that Mary would be immaculately conceived. She was a sinner, just like any other woman. This is further backed by Romans 3:23, which says all have sinned, listing no exceptions.
Catholic objection: Romans 3:23 does not include Jesus, so why does it have to include Mary?
Christian response: Because the rest of scripture demands we exclude Jesus, whereas nothing in scripture ever sets Mary apart from this rule. Furthermore, if we're just excluding people willy nilly, why not exclude other people? Joseph married Mary, and apparently had the self control to lock himself into a marriage devoid of sexual intimacy, so maybe he was also sinless?
Was Mary a perpetual virgin? Matthew 1:24-25 tells us that Joseph "knew her not" (i.e. slept with her) until she had given birth to Jesus. The word "until" tells us that he certainly knew her after Jesus was born, so we can put this one to rest pretty easily, but further evidence comes from the fact that Jesus actually had brothers and sisters (Matthew 13:55-56). One of those brothers, James, even wrote the book that bears his name. As did another bother, Jude.
Catholic objection: They were actually His cousins.
Christian response: There is no context to suggest this, and plenty of contextual clues, such as the fact they were often accompanied by Mary, to suggest that when the Bible says "brothers", it means "brothers". Furthermore, even the Old Testament tells us that Jesus has brothers, His "mother's children", who would actually reject Him (Psalm 69:8). There is no need to try to force Catholic interpretations into the Bible where they are not justified. This is called eisegesis.
Mary's assumption into Heaven follows the same principle as her immaculate conception. Just as immaculate conception isn't a common occurrence, neither is assumption into Heaven, and thus if it was going to happen, God would have alerted a prophet. He didn't. Read the Bible from cover to cover, you won't find it.
Mary's role in redemption is shaky in Catholicism. Catholics tend to get offended if you say they worship Mary, claiming that they only "venerate" her, but a rose by any other name still has some pretty nasty thorns. While there are a variety of Catholic views on Mary's role in salvation, Catholicism always raises her above what she ought to be. Catholics even pray directly to her, saying "Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death. Amen." To a Christian, this prayer should be as repugnant as a prayer to Zeus. Mary the "mother of God"? She was a humble maidservant (Luke 1:48) who was chosen to bear the human incarnation of the already existing (John 1:1) Jesus. That doesn't make her the mother of God, that makes her the mother of Jesus.
There are a myriad of other problems that come with asking Mary to pray for us. The first is that it assumes she can actually hear us. If we assume we can successfully contact her, she won't want us to. Samuel's example is proof of that (1 Samuel 28:15). But not only will Mary not want us praying to her, Jesus won't want us praying to her either. In Isaiah 8:19, Isaiah reasons that seeking the dead (like Mary) on behalf of the living (like us sinners) is absurd, because we ought to seek God, not the dead. In verse 20, he doubles down, declaring "to the law and testimony!" (i.e. the scriptures, which explicitly condemn speaking to the dead), and even going as far as to say that those who say otherwise have no light in them.
Catholic objection: Mary isn't actually dead, just as Abraham is not dead.
Christian response: Much like Abraham, Mary is, in fact, dead. While they live in one sense, it is not the same sense in which we are alive. Scripture clearly records that certain saved figures, including Abraham (Genesis 25:8) died. Furthermore, when Samuel was contacted by Saul, he was pretty ticked off, because Saul should have sought God, and listened to His answer. All of this can be paired with the obvious fact that the law against contacting the dead was given to the children of Israel, i.e. in a land where many people would be saved. The law would be quite different if there was a moral distinction between contacting the dead in Christ and the dead outside. The law is simple: If they're not in this world, let them rest. Mary is dead in the sense that it is an abomination to attempt contact, even on the off chance she could hear us.
Hebrews 4:16 further tells us that we can boldly approach the throne of grace when we need mercy. If Mary could hear us, if she wouldn't be cross that we disturbed her, and if it wasn't outright blasphemy to ask for her intercession when God has the only legitimate claim to our prayers, it would still be pointless. We don't need Mary to pray for us, because we can pray for ourselves. We can go straight to God to ask Him for whatever we need (e.g. Luke 11:11-13). If we are in any way frail in our prayers, it is the Holy Spirit, not Mary or any Saint, who intercedes for us in that regard (Romans 8:26). There is no reason to believe that praying to any dead person will add an ounce of strength to our prayers.
Although not an official doctrine in Catholicism, there is one more blasphemy that many Catholics currently believe, and are pushing to have included in the religion: Mary's role as co-redemtrix. This can be put to rest in one verse: For there is one God and one Mediator between God and men, the Man Christ Jesus (1 Timothy 2:5). Mary never went to the cross. Even if the Romans had killed her in a manner 10 times more brutal than they killed Jesus, Mary would still be insufficient as a mediator because she had her own sins to pay for. Christ, and Christ alone, can redeem man to God.
The Eucharist
The Eucharist is a name given to the Catholic version of communion. In Catholicism, the bread and wine consumed during communion are consecrated by a priest (more on the priesthood later), and then literally become the flesh and blood of Jesus, re-sacrificing Him. This is called "Transubstantiation". In Christianity, not so. First, communion is not a sacrifice. According to Hebrews 7:27, Jesus sacrificed Himself once and for all, succeeding where the previous priesthood failed. Communion is done in remembrance of this (Luke 22:19; 1 Corinthians 11:24), not to "make it present", and certainly not to re-sacrifice Jesus. Jesus Himself said that His flesh and blood are not literally consumed, but that the words He spoke were spirit (John 6:63). Furthermore, blood is considered unclean to the Jews (Leviticus 7:26), and cannibalism, while not explicitly forbidden, is implicitly forbidden through various statements the Bible makes, such as man being made in the image of God (Genesis 9:6), and the fact that cannibalism is always mentioned as a horrible horrible curse (Leviticus 26:29; Deuteronomy 28:53-57; Jeremiah 19:9; Lamentations 2:20; 4:10; Ezekiel 5:10).
Catholic objection: Being hung on a tree is also considered a curse in scripture, so are you saying Jesus was cursed?
Christian answer: Yes... Galatians 3:13.
This alone would make the consumption of Jesus' literal flesh and blood sinful (if it were possible to access His physical body, but as He is not currently on Earth, this is impossible), but further evidence that the apostles didn't take it literally, before or after the resurrection, comes from their reactions to it. As devout Jews, all of the apostles (except, maybe, Judas) would have at least hesitated upon being told they were about to eat Jesus. You can try this today. Find a devout Jew and ask him to eat something unclean. He'll puke at the thought of a bacon sandwich, so how you intend to convince a devout Jew to eat human flesh and drink human blood I don't know.
Furthermore, Peter declares in Acts 10:14 that he has never eaten anything unclean. In this vision, Peter is being directly commanded by God Himself to eat unclean animals, and his response is complete refusal. 3 times, in fact. Peter did not obey the command to "rise, kill and eat" even once. If Peter refused a direct command of God to eat an unclean animal, he would have at least put up a bit of a fight had he believed he was being commanded to eat and drink Jesus' flesh and blood. Remember, this is the same Peter who said Jesus would not be taken to the cross. He is literally famous for resisting some of Jesus' harder teachings, yet we're expected to believe he would have just sat there and drunk what he thought was literally human blood without even saying "Lord... are you sure about this?"
The Priesthood
I mentioned the priesthood in the last section, so here I mention it again. The Catholic priesthood is very different to the Christian priesthood. Most notably, it is a formal position held within the Catholic Church, and priests are addressed as "Father". Priests are also forbidden to marry, and are said to have the power to absolve a Catholic of their sins.
In Christianity, however, the priesthood is not an official Church position. Rather, all believers are priests (1 Peter 2:5-9). I am a priest. If you're a Christian reading this, you are a priest. If you're a Christian who identifies as a Catholic, ironically, you may well be more of a priest than the priest at your church (though I do know of at least one Catholic priest who uses his position to lead his congregation away from the heresy of the Catholic Church and towards Christ, so it is possible to be both). The truth is, even a child, wholly unfamiliar with the more complex doctrines of the Christian faith, can be a priest just by seeking the Kingdom of God.
Furthermore, in Matthew 23:9, Jesus declares "Do not call anyone on earth your father; for One is your Father, He who is in heaven." Evidently, Jesus is not referring to your biological or adoptive father. The paternal figure in your life is your father, and it is impossible to obey the 6th commandment without acknowledging this. Rather, Jesus is referring to the Pharisaical practice of addressing priests as Father, because they believed that since they preached the life-giving words of the scriptures, they were the spiritual fathers of their flock. The Catholic priesthood is almost identical, and is likewise forbidden.
The fact that Catholic priests are forbidden to marry is especially damning to Catholicism. In Christianity, remaining single is considered very noble for those who can accept it (Matthew 19:10-12; 1 Corinthians 7:8), but for those who cannot accept it, it is far better to marry (1 Corinthians 7:9). To that end, the same Paul who wrote "to the unmarried and to the widows: It is good for them if they remain even as I am", also tells us that forbidding people to marry is called a doctrine of demons (1 Timothy 4:1-3).
Finally, although confession to a priest is technically mentioned in the Bible, it is not mentioned as confession to a literal priest who forgives you. Rather, in James 5:16, we are told to confess our sins to each other (and of course, we are all priests), not so that a priest can forgive us, but so that we can pray for each other for healing. The idea that anyone but God can forgive sins is blasphemous (Mark 2:7; Luke 5:21).
The Papacy
The Papacy is the idea that during His ministry, Jesus chose Peter as the primary apostle, and that the Pope is the latest in a long line of successors to Peter's role. Catholics even have a favourite proof text for this one, Matthew 16:18-19, and this is actually the official Catholic interpretation. It was once believed that if you deny this interpretation, or that this has always been the interpretation taken by the Church, you were anathema.
First, I will explain the correct meaning of the proof text. In Matthew 16:18-19, Jesus is not giving Peter primacy over the other apostles. There are four main interpretations as to what "this rock" Jesus was referring to is. The first possible interpretation is that He was referring to Himself. This is possible, because Jesus is the rock (Matthew 7:24-25). The second is that all of the Apostles are the rock, which is defended by the fact that just two chapters later, Jesus gives them the same binding and loosing authority as Peter (Matthew 18:18). Another interpretation is that Peter is the rock, which is possible, as Peter was undeniably a strong figure in the early Church. Remember, there's a difference between "rock" and Pope. But the most likely interpretation, and the one I hold to (as did more than 80% of the so-called Church "Fathers") is that Jesus is referring to Peter's testimony just 2 verses earlier that "You are the Christ, the Son of the living God." This makes sense, not only because the original Greek does not use the same word for Peter as it does for rock, even though Peter does mean rock, but also because it is a continuation of the same account. Jesus is actually responding to Peter's testimony by saying "on this rock". This also explains why Jesus did not say "I tell you, you are the rock, and on you I will build my Church", which would have alleviated 2,000 years of confusion.
So, we see that of the four main interpretations of Matthew 16:18-19, none of them really prove the Papacy. But Catholics argue that because Peter was given the authority to bind and loose things on earth, therefore Peter must have had primacy. Two problems. First, 2 chapters later, Jesus gives all the apostles the same power (Matthew 18:18), yet Catholicism does not hold that there are 12 popes corresponding to the 12 apostles. Second, even the apostles did not interpret it this way, as in Luke 22:24, the apostles argued over which of them would be the greatest. Jesus, of course, rebuked them, reminding them that He had already given Peter that honour. I am, of course, joking. Rather than telling them He had already said Peter was the greatest among them, He told them that to be the greatest, they had to act in the opposite way to the gentiles. With the gentiles, the greater people dominate the lesser, but Jesus pointed out that He was greater than them, and yet He was among them as one who served, thus in order to be considered greater, they had to act as if they weren't. Theoretically, then, Peter could have been the greatest, but only if he was humble enough to out-serve the rest of them. I can tell you this much, most Popes throughout history are not so humble.
Salvation
Let me ask you a question: How do you get to Heaven? If you're a Christian, the answer is simple: confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, and you will be saved (Romans 10:9, emphasis mine). If you're a Catholic, the answer is far more convoluted. Catholicism is a works based faith, and not a simple one. Rather than the usual "do good more good than bad" type thing that is common in most works based religions, Catholicism teaches different degrees of sins, and different ways to absolve them. Specifically, Catholics teach about "mortal" and "venial" sins. A mortal sin is a sin which, if one dies without having such a sin resolved, will earn them a one way ticket to Hell. A venial sin, if unresolved, will simply require some time in Purgatory.
Biblically speaking, Purgatory does not exist. Not only is it not mentioned at all in the Bible, but the concept of a believer spending any time apart from God after death is utter nonsense. 2 Corinthians 5:8 tells us quite clearly that to be absent from the body is to be present with the Lord. There is no waiting period while that packet of crisps you nicked and never told your priest about gets paid for. Just because Father Bob doesn't know you swore at your mother doesn't mean you're not going straight to God's throne when you die. Furthermore, Romans 8:1 tells us there is no condemnation for those who are in Jesus. Not that Jesus paid for some of your sins, but you still need to take care of some yourself. Purgatory is a completely mythical concept that has no place in Christianity.
The idea that one can lose salvation must be terrifying to a Catholic, but for a Christian, it is a fear that is easy to alleviate. While Catholics like Cardinal John O'Connor believe they can "hope, pray and do my very best", but still don't know if they're going to Heaven or Hell, John the Apostle wrote 1 John to we who believe so that we can know we have eternal life (1 John 5:13).
The Catholic belief that you can't know where your going isn't because the Catholic God is capricious, likely to send someone to Hell even if they have fulfilled all His requirements, but because God's requirements simply cannot be met, and yet a Catholic still believes he must meet them in order to be saved. Catholicism teaches a very different "gospel" to the Bible. In Christianity, we are saved by grace, through faith, not of works. Salvation is a gift given to us by God (Ephesians 2:8-9). By definition, if salvation requires works, it is no longer by grace, otherwise grace is no longer grace (Romans 11:6).
The Bible
And so we come full circle, back to Sola Scriptura. The doctrine that the Bible is the sole and sufficient authority of the Christian faith. Clearly, as the above demonstrates, Catholicism does not believe that the Bible alone is sufficient. But I'm going to tell you a belief that all true Catholics hold, but few have the guts to admit. Not only does Catholicism teach that the Bible is not the only authority of the Christian faith, but ultimately, Catholics must believe that it is wrong. Throughout this article, we have briefly examined a number of ways Catholicism contradicts the Bible, and yet so many people, whether Catholic or otherwise, still believe Catholicism is a part of Christianity. And so, I will leave you with this: In 2 Corinthians 11:4, Paul says "For if he who comes preaches another Jesus whom we have not preached, or if you receive a different spirit which you have not received, or a different gospel which you have not accepted—you may well put up with it!" Catholicism hits all three strikes. To one degree or another, it preaches another Jesus, whom Paul did not preach. It preaches a different spirit, whom the Church had not received. It preaches a different gospel, which the Church had not accepted. With a different Jesus, a different spirit, and a different Gospel, Catholicism is a completely different religion from Christianity. It is therefore essential that Catholics repent of professing it, Christians avoid it like paganism, and unbelievers learn to differentiate between the Church of Christ and the Church of Rome.