If you understand how Scripture came to be, you have to at least accept that for a very long time, the Scriptures we all just letters to communities. Even the Gospels took years to find their way into general use by the Christian communities. Until the books of the bible were set upon and generally accepted, they were considered just that, pastoral letters from Apostles to different communities that addressed certain problems, or generally gave support and encouragement (remember, Christians were being persecuted while these letters were being written and circulated). The most reliable form of teaching at the time was word of mouth teaching from the Apostles, then later the Bishops (episcopoi) and deacons (diakonoi) they appointed (Timothy, Philemon, and Stephen are good biblical examples). Now, they had the Old Testament available to them, and the most common form of Scriptures used in the areas that Paul was evangelizing was the Septuagint. Regardless of what one thinks about this version of Scripture, it is historically verifiable that this was the most commonly used version of Scripture at the time. This is why the Gospels of Luke and Mark go through a very detailed lineage of Jesus in their beginings, to show that their new message (the Gospel) was in synch with established belief. Paul debates with the Thessalonians for weeks before they reject his new teaching (oral tradition). The Bereans accept it, and are considered noble for it. But the fact of the matter remains, if you were to go by the letter of the established canon, there was something about the new message that was objectionable, therefore people who came to faith, did so in a combination of oral tradition and Inspired Scripture. The two are inseparable.
It can be looked at this way, the Catholics have a particular tradition (a way of viewing, interpreting, and explaining the Scrtipures), Lutherans do as well. The congregants of a non-denominational, full-gospel, open-bible church do too, they operate under the tradition of the pastor. If you reject all of them, then you are operating under your own tradition.