9. Holding fast—Holding firmly to (compare Mt 6:24; Lu 16:13).
the faithful—true and trustworthy (1Ti 1:15).
word as he has been taught—literally, "the word (which is) according to the teaching" which he has received (compare 1Ti 4:6, end; 2Ti 3:14).
by—Translate as Greek, "to exhort in doctrine (instruction) which is sound"; sound doctrine or instruction is the element IN which his exhorting is to have place … On "sound" (peculiar to the Pastoral Epistles), see 1Ti 1:10; 6:3.
convince—rather, "reprove" [Alford], (Tit 1:13).