Strictly speaking, it doesnāt. If you preach that Christ was crucified for sinners, raised for their justification and ascended into heaven, you are preaching revelation, I.e., the word of God. The issue, then, is whether at present there is revelation from God apart from what is written down. In order to demonstrate that a doctrine not written down is revelation, it must be shown to come from the apostles. It is the Protestant contention than many RCC distintictives do not. It is well established that the Scriptures did. That is why anything apart from them are subject to their authority.