Most Protestants believe that the Bible is the pillar and foundation of the truth, and no knowledge outside of the Bible is necessary for our salvation. But then why does Saint Paul write that the Church, and not the Bible, is the pillar and foundation of the truth? This is a powerful text that refutes the Protestant theory of sola Scriptura (Scripture alone) which erroneously holds that the Bible is the sole source of Christian truth (a theory which cannot be found anywhere in the Scriptures). Instead, Saint Paul says the Church is the pillar and bulwark of the truth.
This means that all the truth Jesus left us concerning faith, morality and our salvation flows from a living Church which, as we have learned, is built by Christ upon the rock of Peter and his successors. As the Catholic Church teaches, God has given us His truth in the form of the living word (written Scriptures and oral tradition) and the living teaching authority of the Church, endowed with the gift of binding and loosing. In fact, it is because the Church is the foundation of truth that we believe in the Bible. This is because the Catholic Church put the Bible together by determining which books were inspired and which books were not. The Church completed its selection of the "canon of Scripture" at the end of the fourth century. If the Catholic Church were not the pinnacle and bulwark of the truth, our belief in the Bible would be without foundation.
The Church's compilation of the Bible illuminates the error of sola Scriptura. As alluded to above, Protestants generally believe that God has revealed everything that is necessary for our salvation through the Bible alone. Consequently, they also believe that no knowledge found outside of the Bible regarding the Christian faith is necessary for our salvation. However, the knowledge of which Scriptures belong in the Bible and which Scriptures do not is necessary for our salvation because if we didn't know this we could be led into error. Further, this knowledge could only come from God because human beings cannot necessarily discern divine inspiration.
The problem, therefore, with sola Scriptura, is that the knowledge of which Scriptures are inspired and which ones are not is not contained in the Bible. The Bible does not have an "inspired table of contents." Instead, this knowledge of the canon of Scripture is a revelation from God that is necessary for our salvation, and yet came to us from outside the Bible . This revelation was given to the Holy Catholic Church, and this historical and theological fact destroys the doctrine of sola Scriptura (interestingly, while Protestants reject the authority of the Catholic Church on most matters, they accept her authority in determining the New Testament canon of Scripture; we pejoratively call such picking and choosing which doctrines to believe and which doctrines to reject "Cafeteria Catholicism").
If I were a Protestant trying to prove sola Scriptura, and there was a verse that said "the Bible is the pillar and bulwark of the truth," I would be proclaiming that verse from the roof tops. At the same time, if I were a Protestant, I would have to ignore 1 Timothy 3:15 to continue my protest of the Catholic faith.
http://www.scripturecatholic.com/my_top_ten.html

