I make known (γνωριζω). See on 1. Corinthians 12:3 for this common verb. As if in reproach.

The gospel which I preached unto you (το ευαγγελιον ο ευηγγελισαμην υμιν). Cognate accusative, "the gospel which I gospelized unto you." Note augment η after ευ- like compound verb with preposition. Note repetition of relative (ο, εν ωι, δ ου, and τιν like relative) without κα (and), asyndeton.