We are to believe it and live it.
John wrote Revelations after many of the Disciples were martyred and had already written their Gospels or letters to reflect that oral tradition.
Yes, Catholics wrote down their oral tradition and protected it via the magisterium.
Let’s go to a higher authority. What does Jesus say about traditions? Will you accept this authority? What is Jesus saying here?
Pay attention to the words, substitute, sidestep, cancel, violate. I believe in the Holy catholic (universal) church. These words apply to all of us.
(Mark 7:9) Then He said, “You skillfully sidestep God’s law in order to hold on to your own tradition.
(Mark 7:13) And so you cancel the word of God in order to hand down your own tradition. And this is only one example among many others.”
(Matthew 15:3) Jesus replied, “And why do you, by your traditions, violate the direct commandments of God?