That the Scriptures were never intended to teach complete Christian doctrine:

“Hence it is plain that the Apostles did not deliver to us everything by their epistles, but many things without writing. These are equally to be believed. Wherefore let us believe the tradition of the Church. It is tradition. Seek no further.”

St John Chrysostom, (commenting on 2 Thess. 2:14)  Hom. 2 Thess.