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. Holding fast the faithful word - Conscientiously retaining, and zealously maintaining, the true Christian doctrine, κατα την διδαχην, according to the instructions, or according to the institutions, form of sound doctrine, or confession of faith, which I have delivered to thee.
That he may be able by sound doctrine - If the doctrine be not sound, vain is the profession of it, and vain its influence. It is good to be zealously affected in a good thing; but zeal for what is not of God will do no good to the souls of men, how sincere soever that zeal may be.
To exhort - Them to hold the faith, that they may persevere.
And to convince - Refute the objections, confound the sophistry, and convert the gainsayers; and thus defend the truth.