Titus 1:9

Holding fast the faithful word, as he hath been taught; no airy, uncertain man, that is of that opinion which his company is of, or his age favours, but holding steady the word of faith, as he hath learned it from me, and the rest of the apostles. That he may be able by sound doctrine, both to exhort, his work is to persuade others to the faith, and to convince the gainsayers; by sound arguments to convince those that speak contrary to it; and if he himself be ignorant of, or uncertain, as to that, how can he ever discharge this employment?