To make it simple, what I’m asking is: if you believe the Catholic Church has the authority to define the Christian canon, because the Christian canon states the Church is the “pillar & shield of the truth,” then how do you which religious “church” has the authority to define the canon? Remember, if the “Church” defines the canon, that means the canon that defines what the Church is hadn’t been “defined” yet. Which came first, the Church or the canon? If you say the Church, then how do you know that unless an established canon was already formed prior to the existence of the Church?
The answer lies in your question. We don’t believe that the Church is the pillar and foundation, merely because the Bible says it is. The Bible affirms and supports the Church, the church doesn’t owe its existence to the Bible.
For example, one can say that the Bible didn’t come down from heaven in any form, therefore it was written by fallible men, who formed fallible churches, who wrote the fallible book, to give themselves infallibility.
Yet, as a Christian you know this isn’t the case and as a believer, you probably know how to answer this question and yet you ask it of Catholics as if it’s unique to our Church alone.
So the question you should ask yourself is this:
Do you believe in the Bible as the inerrant, God breathed book that it is or do you merely believe in the Bible, because the Bible
itself says that it is the inerrant God breathed book that it is?
The Bible can’t authenticate itself, so there must be another Holy Spirit guided entity to affirm that what we have, is in fact the Holy Word of God.
The Protestant answer is to acknowledge that the
early church was that Church, but it fell under corruption and pagan influence, usually around the time of Constantine, and the RCC rose to power and as you say, added books to the original canon. Luther simply brought back the original early church canon and tried to restore the church to its roots.
The problem is that there is no irrefutable evidence that such a thing ever occurred. Because now we are left trying to decide what happened to the early Church and who should we look to as the pillar and foundation of truth? As you asked above, which Church?
I know of only one that still insists and supports that they are that Church and has existed for over 2000 years and can trace its origins back to that same early Church.