As the Gospel is the most essential issue in the Christian faith, the biggest criticism of the Catholic Church is that it seriously perverts it. How? By adding works to it. On top of faith, the Catholic Church preaches a number of works one must do in order to receive salvation. Even then, one has no assurance of salvation until one actually makes it to Heaven. To say "I am going to Heaven" is the "sin of presumption".
The irony is, just as Catholics do not understand the Gospel, they also do not understand Christian criticisms of their false gospel. It is entirely accurate to say the Catholic Church teaches salvation by works, simply because there are works the Catholic Church teaches you must do in order to be saved. However, in spite of its accuracy, it is also too simplistic. Simply saying "salvation by works" may make it sound as if works alone are sufficient, which is not what the Catholic Church teaches.
Now, the irony here is there are exceptions. Most notably, a little boy once asked Pope Francis about the salvation of his father, who had sadly died as an unbeliever. The Pope told him "God surely was proud of your father, because it is easier as a believer to baptize your children than to baptize them when you are not a believer. Surely this pleased God very much." He also said "talk to your dad; pray to your dad."
Skipping over the absolute abomination of talking to the dead (Deuteronomy 18:9-12, Isaiah 8:19-20), even if the deceased happen to be Godly believers enjoying their eternal rest with God (1 Samuel 28:15), which Catholics make a detestable habit of, it is just an unfortunate fact that, in spite of what Catechism of the Catholic Church teaches, there is no way to be saved apart from Christ. So, even though the Bible teaches we are saved by grace, through faith, apart from works, Pope Francis, if only for a brief moment, taught a young boy that his father was saved by works, apart from faith!
But Catholics can, ironically, afford to ignore the major blunders of their "Holy Father". What they cannot afford to ignore, however, is the Bible. Not that they don't, but it is inconsistent with their religion to do so. But what does the Bible teach about works and their relationship to salvation?
The irony is, the only time works are directly and inseparably tied to salvation in scripture is when we are told they are why we need salvation in the first place. We are told that all have sinned and fallen short of the glory of God (Romans 3:23), and the wages of sin is death (Romans 6:23). Even our righteousness, because of our sins, is filthy rags (Isaiah 64:6). Therefore, we are saved not by works, but by grace, through faith (Ephesians 2:8-9). We then do good works not to get saved, but because we are saved (Ephesians 2:10).
Catholics still take issue with this, however. In their mind, although scripture so clearly teaches that we are saved by grace, through faith, not of works, "faith without works is dead" (James 2:17, 20, 26), and so if we are saved by faith, which logically cannot be alone, we cannot be saved by faith alone. Right?
There are three main problems with this. First, James is not an alien. The scripture penned by his hands is inspired (2 Timothy 3:16) by the same God who cannot deny Himself (2 Timothy 2:13). Therefore, if we accept (as, of course, I do) that James is scripture, it cannot contradict the rest of scripture. Yet, scripture endlessly affirms that salvation is by grace, through faith, not of works. Every book apart from James teaches that works are not required for salvation, and so James cannot be teaching that salvation does require works.
The second problem is that the same Paul who wrote Ephesians also wrote Romans. Look what he writes in Romans 5:18-6:4: "Therefore, as through one man’s offense judgment came to all men, resulting in condemnation, even so through one Man’s righteous act the free gift came to all men, resulting in justification of life. For as by one man’s disobedience many were made sinners, so also by one Man’s obedience many will be made righteous. Moreover the law entered that the offense might abound. But where sin abounded, grace abounded much more, so that as sin reigned in death, even so grace might reign through righteousness to eternal life through Jesus Christ our Lord.
What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it? Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life."
In this short extract, the entire Catholic Gospel crumbles. Note, first of all, how we are told that by one Man's obedience (of course, Christ's), many will be made righteous. It is Christ's obedience, not our own, which saves us. Catholics can actually be quite grateful for this, as obedience to the Catholic Church requires disobedience to God.
Furthermore, notice Paul's follow up. "Shall we continue in sin that grace may abound?" Would the Catholic "gospel" merit that objection? No, of course not! But as the Gospel teaches that one is saved apart from works, the logical conclusion is that one could continue in sin and rely on grace. And so Paul refutes this idea. But not by saying "you absolute dumpling, if you continue in sin, grace will not abound, you'll lose salvation". Instead, He reminds us what we are saved to. We have eternal life, therefore we should walk in life.
As for salvation by grace and works, this same Apostle, in the same book, tells us "And if by grace, then it is no longer of works; otherwise grace is no longer grace. But if it is of works, it is no longer grace; otherwise work is no longer work." (Romans 11:6). This single verse utterly demolishes any link between grace and works. As you cannot pay for that which is free, so also can you not earn grace through any amount of works.
Which brings us to a theme you may well have noticed throughout this article. Salvation is called a gift in scripture. Tell me, who earns a gift? The giver, or the receiver? Gifts, by their nature, are free for the receiver. How rude it would be for the receiver to claim to have merited the gift. How much greater does this rudeness seem when the greatness of the gift increases? If I gave someone a key ring, I would be offended if they claimed to have earned it. If I gave them an expensive piece of jewelry, more so. But Jesus, beyond all imagination, left the riches of Heaven, the glory of His Father, to live in human flesh, and as nothing but the (apparently illegitimate) son of a carpenter, only to die on a cross for sins we committed. How utterly detestable for us to then turn around and say that's not enough; we must continue to work for salvation!
There can be no doubt, the Gospel leads to works. Nevertheless, in order to be saved, the Bible lays no greater burden on us than this: "...Believe on the Lord Jesus Christ, and you will be saved..." (Acts 16:30-31).
Biblically speaking, therefore, if you believe in salvation by works at all, you believe in salvation by works. You can't be saved by both grace and works, they cancel each other out. Therefore, you can only have one. But your works cannot save you. They are exactly why you must be saved in the first place. The Catholic gospel, therefore, is a false one, and those who preach it, by Paul's divinely inspired reckoning, are anathema (Galatians 1:8). It is essential for Catholics to repent of this grievous sin.