“Now, Jesus did many other signs in the presence of the disciples, which are not written in this book; but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in His Name.”
John, towards the end of His Gospel, gives us these words. And there is a contrast set forth - two clauses. John notes that there is more that the disciples saw that isn't written. John notes that what is written is written for belief and salvation.
Which clause is more important?
This is what I find frustrating about so many of the Tradition vs. Scripture battles that come along. They end up moving into the realm of whether or not tradition is valuable, whether or not it is true, how much we use it. It puts all the emphasis and focus on that first clause -- is this part of that other stuff that the disciples saw, is this stuff that is rightly handed down?
We can surmise, we can come up with guesses - we can delight, even. (I myself love the tale of John refusing to enter the Bath when he sees the gnostic leaving - and on Christmas day the tale of Satan smacking the guy who doesn't doff his cap at "Homo factus est"). But is tradition and its veracity the thrust and focus?
It isn't for John. Yes, there is other stuff - but this, this here, this Gospel is written so that you may believe in Christ and have eternal life. The other stuff is nice, may be nice, but the meat, the real McCoy is here in the Word. If you want surety, if you want something concrete, go to the Word, because it has what you need.
Tradition informs. Tradition may safeguard. Tradition may even protect errors that have crept into the Church over time, (for as we see in John 21:23 - the brothers are capable of twisting the oral tradition as well). But the Word of God gives what we need.
While we make use of the first clause, we live in the second.