2 Thessalonians 2:15
So then, brethren, stand firm and hold to the traditions which you were taught by us, either by word of mouth or by letter.
This passage is one of texts that bears the strongest witness to the fact that the apostles did not simply hand the gospel down to us by writing Scripture, but by handing on a whole life in the Sacred Tradition of the Church. The Tradition handed down by “word of mouth” refers to the whole unwritten Tradition”the common life, worship, and teaching of the apostolic college”which was handed to the Church in union with the inspired writings of the apostles and their cohorts. Why did they do things this way and not just write everything down? Because they were handing on the Way, the Truth and the Life, not just a legal brief, a technical manual, a theological treatise, or a copybook of Improving Maxims. Just as parents do not issue handbooks filled with detailed instructions, philosophical proofs, and studies in case law in order to pass on who they are and what they believe to their children, so the apostles did not limit the way in which they communicated the Life which had been entrusted to them to merely written form. God revealed himself in a human way in Christ, so the apostles passed him on to the Church in a human way too: a way which included, but was not limited to, the written word.