"But without faith it is impossible to please Him, for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him." - Hebrews 11:6
If you were to cite this verse to an atheist, it wouldn't mean a huge amount to him. As Christians, we of course believe that the Bible is true, and God does, indeed, exist, and reward those who diligently seek Him. Furthermore, we believe that the Bible is His infallible word, upon which we can rely entirely. An atheist, however, does not recognise the authority of Scripture, and so its repeated affirmations that God exists, and rewards those who diligently seek Him, will not convince an atheist to do so.
Just as atheists and Christians view the authority of Scripture differently, so also do Catholics. Unlike atheists, Catholics do recognise the inspiration of Scripture. However, they have also placed what they call "sacred tradition" on its level, and have declared that their Church alone has the authority to interpret it. The Bible, in their view, came from, supports, and even gets its authority from their Church, and therefore, they should be immune from its tests.
Of course, if this was true, the Catholic Church wouldn't need immunity to the Bible's tests, because, much as Paul did in Acts 17, it would pass with flying colors. At the very least, the Catholic interpretation would fit the words on the page. But more often than not, we find that the Catholic Church conflicts with Scripture. Yet, when we go to Catholics and point these things out, they invoke their imaginary authority, which they base on a revised version of history.
By contrast, the Christian view is "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." (2 Timothy 3:16-17), and "Do not add to His words, Lest He rebuke you, and you be found a liar." (Proverbs 30:6).
During the Reformation, an era in which the Catholic Church was politically and culturally dominant in the Western World, this concept became known as "Sola Scriptura". Sola Scriptura is a Latin term, literally meaning "Scripture alone", effectively meaning Scripture alone is the measure of all things Christian. It does not, and indeed has never meant, that Scripture alone is true, or useful. It does, however, mean that Scripture alone defines the Christian faith.
Much like other Christian doctrines the Catholic Church doesn't like, the Catholic Church claims this is an innovation of the Reformation. It did not exist before the Reformation, and was invented during the Reformation. By contrast, they claim, history shows that the Catholic Church was the Church Jesus founded, and the only real "changes" have been the clarification of existing doctrines, much like the Trinity. As John Henry Newman famously put it, "to be deep in history is to cease to be Protestant".
Of course, simply studying Scripture will deny this absurd conclusion. It does not say what Catholics say it says. Every time we open the Bible and find it in direct conflict with the Catholic faith, we have all the evidence we will ever need against the Catholic faith. We do not need to study history any further, because history is just a description of past events, not a prescription for repeating them.
Nevertheless, Catholics do place a heavier emphasis on history, and in particular the so-called Church "Fathers", than they ought. This, I believe, is because of the great ease with which one may access Scripture, but relative rarity of Christians who study the Church "Fathers". Beating a Christian on their home turf (the Bible) is very difficult, but not as many Christians will know what the Church "Fathers" taught. And indeed, if they give them any credibility, it can be quite daunting when they said something that, at the very least, appears supportive of the Catholic Church. Thus, although the Church "Fathers" have no authority, it can be helpful to know what they said, if for no other reason than to knock a Catholic off his high horse.
See, contrary to the Catholic narrative, the first 1500 years of Church history is not unanimously Catholic. This can be expected, as of course the Bible is the earliest, and most authoritative Christian source, yet the Catholic Church and its unique doctrines are entirely absent, if not flat out refuted, whereas Sola Scriptura and the like are right there, in black and white. But it is "surprisingly" common for Church "Fathers" to hold the same beliefs as Christians, and even use the same Scriptures to justify those beliefs.
An excellent example of this is Cyril of Alexandria (375 - 444 A.D.). who wrote "Sufficient, sufficient for this are the Scriptures of the holy Fathers, which if anyone will diligently study, he would immediately have his mind filled with divine light. For, they did not speak of themselves, but 'all Scripture is given by inspiration of God, and is profitable.'"
Notice, this is the same verse I quoted earlier. I used 2 Timothy 3:16-17, and here, Cyril of Alexandria likewise quotes it in the same context. This is the same man who rhetorically asks "How can we prove and certify as true something which Sacred Scripture does not attest?"
The simple fact is, we have an embarrassment of riches when it comes to Church "Fathers" who believed the Scriptures were the supreme authority in the Christian faith. Augustine, Jerome, and Irenaeus are among the big names who professed the doctrine. Of course, Catholics often argue that they did not, claiming they are cited out of context. Yet, ironically, the only way I've seen them do this is to cite them out of context.
Now, I don't claim to be an expert on the Church "Fathers" by any means. Nor do I have any desire to study them in much more depth than I already have. Their writings do not affect my personal faith, my life, or my apologetics strategy. Everything in me wants to just stick to God's Holy word. And if Catholics have any confidence in their theology, so should they. But because they know they can't do that, they want to go to the Church "Fathers". Yet, when we do go to the Church "Fathers", they tell us to go right back to the Bible, which we should never have left in the first place.
But we all know why we did leave it. The Bible has always been the bane of the Catholic Church. You won't find Catholic Mariology there. Nor will you find the mythical realm of Purgatory. The bread and wine consumed at communion are, indeed, just bread and wine, designed to symbolise the Lord's flesh and blood, not actually become it. The Pope is not the head of the Church, nor is there a special class of priests, for the whole Church are priests, and we are absolutely not addressed as "Father".
Most importantly, when we read the Bible, we genuinely do find a Gospel of salvation by grace alone, through faith alone, not of works. While Catholics are more than capable of finding a few verses to cite out of context, the Bible is clear throughout. No one reading it honestly will draw another conclusion. Therefore, Catholics are in desperate need of repentance, for Scripture warns us very clearly: There is one Gospel, and deviation from it is damning.