Catholics have a very nasty habit of overestimating their Church's significance. Some of them even argue that without their Church, one would not know about the Trinity. I remember one example of a Catholic I debated. He started bragging that without the Catholic Church, I wouldn't know any theology, and he challenged me to defend the Trinity without referencing a Catholic document. Of course, I was able to defend the Trinity exclusively with scripture. His response? "No no, the Bible is a Catholic book. Try again."
For purposes of this article, we can ignore the circular reasoning of claiming the Bible is a Catholic book in an attempt to prove the Bible is a Catholic book. Let us instead ask, if the Bible really is a Catholic book, would it not read like one?
To clarify, I do not mean there are no similarities between the Bible and actual Catholic works. The Catholic Church is not yet so far removed from Christianity that it completely lacks similar themes, and some Catholic works even directly quote scripture. However, this is to be expected. The Qur'an, the Book of Mormon, and other blatantly non-Christian works, can often read like the Bible. But this is because they read like the Bible, not because the Bible reads like them. Imitation is the greatest form of flattery, Satan's ministers appear as ministers of righteousness (2 Corinthians 11:14-15), and Satan himself, in his pride, declared that he would be like the Most High (Isaiah 14:14). It is no surprise, then, that we see some Bible in Catholicism.
What we do not see, however, is Catholicism in the Bible. To illustrate this, consider the aforementioned religious works. If one ever questioned the Islamic nature of the Qur'an, would they be able to maintain that view? If it was ever claimed that the Book of Mormon was not a Mormon book, how long would such a claim last? Indeed, if ever there was a dispute that the Catechism of the Catholic Church was a Catholic book, could such a dispute not be solved swiftly and firmly?
With regard to the Catechism, the title alone sets it apart as Catholic. But even if it were to fade into obscurity, and 2,000 years from now, it was renamed "Catechism of the Evangelical Church", one would be able to immediately detect the changed title just by reading the book. It even says "This catechism aims at presenting an organic synthesis of the essential and fundamental contents of Catholic doctrine, as regards both faith and morals, in the light of the Second Vatican Council and the whole of the Church's Tradition." But setting that aside, it really does fulfil that purpose. It does talk about Purgatory, it does talk about the 7 Sacraments, it does talk about the Papacy, it does talk about the 4 Marian dogmas etc. It's all right there, in black and white.
But not in the Bible.
The Catechism of the Catholic Church is self evidently a Catholic book because it is titled after its Catholic faith, it is promulgated by Catholic authority, and it describes, in much detail, Catholic doctrines. The Bible, by contrast, is self evidently not a Catholic book. Aside from the fact Catholicism's unique doctrines are completely absent, the Bible frequently finds itself in conflict with the Catholic Church, from the minor (e.g. the perpetual virginity of Mary) to the very Gospel itself!
When it comes to the minor, there isn't really a problem until the Catholic Church suggests Christians must believe their errors. All denominations have their shortcomings (which is why I, personally, don't claim one), but the Catholic Church claims to be the authoritative one. Now, if one wants to believe in the perpetual virginity dogma, I really don't care. It's false, as scripture clearly tells us that Mary married (Matthew 1:20-24), had legitimate marital relations (Matthew 1:25), and bore children (Matthew 12:46; 13:55-56; Luke 8:19; Mark 3:31) with Joseph. But no one goes to Hell for believing Mary and Joseph never consummated their marriage. It's just incredibly strange and contrary to all Biblical evidence.
Of far greater importance, however, is the path to salvation. On this, the Bible is exceptionally clear. In Christianity, we are saved by grace, through faith, as the gift of God, not of works, lest anyone should boast. How do I know that? Because the Bible explicitly says "For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast. For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them." (Ephesians 2:8-10). According to the Council of Trent, however, those who affirm this are anathema. The irony, however, is that according to Paul in Galatians, this makes them anathema (Galatians 1:8). Not even an Apostle, not even an angel from Heaven, has the right to alter the Gospel as it is presented in the pages of scripture.
But the pages of scripture present a distinctly non-Catholic Gospel. It presents a Gospel that is made effective by faith alone. It presents a Gospel that leads to good works, rather than being fuelled by them. It presents a Gospel of security. The Gospel presented in the Bible is far greater than the convoluted "gospel" of the Catholic Church.
"Not so!", says the Catholic. The Bible is a Catholic book, after all. So obviously, everything I just said is wrong. The Catholic Church rejects Sola Scriptura, so they don't believe it needs to present Catholic doctrine clearly, but they still claim it does so to some extent. They certainly don't believe it agrees with me, or that it disagrees with them. So here's my question: Why do we need them to tell us that?
Whenever a Catholic tells us the Bible is a Catholic document, they are unwittingly confessing that it isn't. If I wanted to know what the Catholic Church teaches, I could simply open the Catechism, and there it is, plain as day, Catholic teaching. I don't (often) need to wrestle with them over where it came from. It was promulgated by Pope John Paul II, who was the Pope at the time, in 1992. But I don't typically have to tell Catholics that. It's a Catholic book, self evidently so. But they have to tell me the Bible is a Catholic book because it self evidently isn't. If it was a Catholic book, I could open it as easily as I open the Catechism of the Catholic Church and see oh, yes, this is clearly a Catholic book. And boom, I'm Catholic, because why in the world would I want to disobey the inspired word of God?
But this cannot be done. I do not open the Bible and conclude it is a Catholic book, precisely because it is not. The Bible, much like the other works we have discussed here today, consists of actual words. And words have meanings. When words are arranged in a specific way, they form sentences, paragraphs, chapters, books, which have a very limited number of valid interpretations. You can't open Genesis 1 and expect to find a recipe for Grandma's lemon sponge cake. You can't open Matthew 1 and use it to pass your driving test. In Revelation 22, can one rightly conclude Satan has a 50/50 shot of winning?
Let's put it another way. Can you open your Bible and insert the Islamic idea that Allah rescued Jesus, placing in His stead some other poor person on the cross and making it appear Jesus was crucified? No sane Catholic would answer "sure, that's a totally valid interpretation unless you appeal to Catholic tradition". But they might as well. The way Catholics talk about "40,000 Protestant denominations", you'd think they believe, without their help, the Bible is so unintelligible it looks like a cat walked across a keyboard.
But it's not. Put simply, the Bible is not a Catholic book. No one, being culturally isolated from the Catholic Church yet having access to the Bible, seeks out the Catholic Church. No one, being ignorant of the teachings of the Catholic Church, will read the Bible and draw uniquely Catholic conclusions. Many Catholics, purely by reading the Bible, have come to reject the Catholic Church. If the Bible really was a Catholic document, why is it not self evidently Catholic? Why is it whenever I open my Bible and simply read, I end up drawing some very non-Catholic conclusions? Is God so incompetent an Author that His divine word needs your supplements? Did He say one thing, but needs you to explain that He meant another? Or is it perhaps more likely that the Bible means what it says? Thankfully, what it says is greater than what Catholicism teaches by far, and anyone with a Bible can prove it.