If we believe not, yet he abideth faithful: he cannot deny himself.

People's New Testament

2:13 If we believe not, yet he abideth faithful. If we prove faithless, he will still be faithful to keep every promise he has made.

Wesley's Notes

2:13 If we believe not - That is, though some believe not, God will make good all his promises to them that do believe. He cannot deny himself - His word cannot fail.

Jamieson-Fausset-Brown Bible Commentary

13. believe not-"If we are unbelievers (literally, 'unfaithful'), He remains faithful" (De 7:9, 10). The oldest manuscripts read, "For He cannot (it is an impossibility that He should) deny Himself." He cannot be unfaithful to His word that He will deny those who deny Him, though we be not faithful to our profession of faith in Him (Ro 3:3). Three things are impossible to God, to die, to lie, and to be deceived [Augustine, The Creed, 1.1], (Heb 6:18). This impossibility is not one of infirmity, but of infinite power and majesty. Also, indirectly, comfort is suggested to believers, that He is faithful to His promises to them; at the same time that apostates are shaken out of their self-deceiving fancy, that because they change, Christ similarly may change. A warning to Timothy to be steadfast in the faith.

Matthew Henry's Concise Commentary

2:8-13 Let suffering saints remember, and look to Jesus, the Author and Finisher of their faith, who for the joy that was set before him, endured the cross, despised the shame, and is now set down at the right hand of the throne of God. We must not think it strange if the best men meet with the worst treatment; but this is cheering, that the word of God is not bound. Here we see the real and true cause of the apostle's suffering trouble in, or for, the sake of the gospel. If we are dead to this world, its pleasures, profits, and honours, we shall be for ever with Christ in a better world. He is faithful to his threatenings, and faithful to his promises. This truth makes sure the unbeliever's condemnation, and the believer's salvation.