He must hold firmly to the faithful word as it was taught, so that he can encourage others by sound teaching and refute those who contradict it.
KJV
Holding fast the faithful word as he hath been taught, that he may be able by sound doctrine both to exhort and to convince the gainsayers.
ASV
holding to the faithful word which is according to the teaching, that he may be able both to exhort in the sound doctrine, and to convict the gainsayers.