2 Timothy 2:13

If we believe not, yet he abideth faithful
The Syriac and Ethiopic versions read, "if we believe not him". This may be understood, either of such who are altogether destitute of faith, who do not believe in Christ at all; and particularly do not believe what was just now said concerning his denying such that deny him, but mock and scoff at his coming, and at a future judgment: this unbelief of theirs will not make void his faith or faithfulness; see ( Romans 3:3 ) , he will abide faithful to his word of threatening; and what he says in ( Mark 16:16 ) will be found to be an everlasting truth: or it may be understood of true believers, whose faith sometimes is very low, as to its exercise on Christ, and with reference to their future glory and happiness; but Christ is faithful to all his, covenant engagements for them, to bring them to glory, and to every word of promise concerning their happiness, and to every branch of the faithful saying above mentioned; and he is ever the same in his love to them, and in the efficacy of his blood, righteousness, and sacrifice; and his salvation is an everlasting and unchangeable one; nor do the saints' interest in it, and security by it, depend upon their acts of believing, or their frames, but upon the firmness and unchangeableness of Christ, the object of faith.

He cannot deny himself;
he cannot go contrary to his word; that would be to act contrary to his nature and perfections, and would be a denying of himself, which is not possible; wherefore his faithfulness will never fail, even though, the faith of his people does, as to the exercise of it.