What if the gospels were designed to train disciples which
were actually supposed to be future rabbis? And then the Epistles were designed
to equip the saints? This would help explain why the word disciple disappears
in the Epistles.
Jesus was training disciples--these are people who would become teachers in the movement that He was beginning. The epistles seem more focused on equipping the saints, rather than training disciples. The word disciple seems to be replaced with saints as the recipients of the literature of the New Testament.
Lots more could be said about this.