Many Apostles did not write epistles. Where are their teachings? Where is the work of the Divine Inspiration in them? Where is the work of the Holy Spirit who speaks through the prophets? It is not possible that some of the Apostles taught only what they wrote. It is not possible that James the Apostle's teaching was only limited to one Epistle nor is it possible that Jude the Apostle taught just one chapter. What about the rest of the eleven Apostles of whose teachings we have received no word? What did they preach? What did they leave for the Church? Most probably those teachings, or some thereof, have reached us through Tradition.