As we discussed in the article on Scripture, the Bible is the final and best source of God's Word. But we all know that given enough time, men will claim they have additional revelation from God—it could be new information, or it could be old information not previously disclosed. It's this latter claim that defines Roman Catholic Tradition.

Think about the various Marian dogmas: an immaculate conception, assumed bodily into Heaven, etc. These teachings cannot be found anywhere in Scripture at all. As time marched on, Catholic theologians developed these teachings by implying they exist in nascent form in Scripture (think about Mary as the Ark of the Covenant) as a type or shadow. Contemporary Catholic scholars like Brant Pitre at Augustine Institute excel at developing a very vague form of reference to Mary, and then expand on that.

Finally, given enough time and authority, we have the Marian decrees of Vatican I, where these dogmas of Mary are declared binding on Catholic faith. All this took place without ever revealing any authoritative Biblical instruction!