Wonderful article on Gnosticism in the early church and how the scriptures were clearly preserved by God. Unfortunately we still find Gnosticism today.
This situation becomes tricky to defend if one does not clearly explain that the Church (notice the capital) set down what was canon and what was not (sorry Gospel of Thomas, you lose.) From day one the Magesterium of the Church set the rules to play by. What was their authority? The Church were headed by the sucessor of Peter. End of the story.
This Church needs no adjective like Catholic, Orthodox or Protestant because humans had not the time yet to smash it into 26,000 sects.