and not trust the rest of what they handed down to us?
Too many years, too many hands and too much unknown. Some of it may be true and other parts less so. God has given us what He wants us to have. I am satisfied what He gives. Blessed be His Name and His Word.
It is precious and wonderful that you have "part" of God's word, the written Scriptures (although not even all of that, since as I am pretty sure that the Bible you use had seven books cut out of it: so you're not even in possession of "*ALL* of Scripture...")
But even if you did have the complete 46 books of the OT, you still wouldn't have the whole Word, which was entrusted to the Church in the preaching and in the practice as well as in the books of Scripture. Scripture itself had its origin from God in the preaching and the practice of the Church.
Tell me: how do you know that Matthew, Mark, Luke and John wrote the four Gospels? The manuscripts of the Gospels are anonymous: they are neither signed nor labeled with their names. So how do you know who the authors were?