From First and Second Timothy, Titus by George T. Montague, commenting on 2 Timothy 2:8-13
If for the Christian, dying with Christ is past (the baptismal understanding of this death is obvious from the past tense: “we have died”) and the resurrection is future, what is the present life? To persevere or “endure.” It is the characteristic of love to endure all things (1 Cor 13:7).
The virtue of endurance (hypomone) appears in the noun form fifteen times in the Pauline letters and here in the verb form. The Church soon found out that those who receive the word do not always persevere. A momentary spiritual thrill may quickly fade, like the seed that falls by the wayside or onto rocks or into weeds. Only the persevering bear fruit for eternal life (Luke 8:15). It is this virtue, born of supernatural hope (1 Thess 1:3), that enables Christians, like Paul, to bear contradictions, trials, and weaknesses (1 Cor 4:9–13; 2 Cor 6:4), because they do so in union with Christ (1:5; Col 1:24) and in the assurance of the divine promise: we shall . . .reign with him.
But Paul is aware that defection and desertion are possible: but if we deny him. In fact, he has experienced both recently, as the two letters to Timothy attest. He is not thinking in particular, however, of the judgment that may fall on his betrayers (2 Tim 4:14); rather he is thinking of the unspeakable disaster that would befall any disciple who would deny the Lord: he will deny us.
It is the same warning expressed in Matt 10:33: “Whoever denies me before others, I will deny before my heavenly Father.” Given the contrast here with perseverance, the meaning is probably not so much a malicious denial as a sin of cowardice, the kind of weakness Peter showed in denying his Lord. Though the early Church hesitated for some time about reconciling those who repented of their denial of Christ during persecution, at length she came to the conclusion that she could do no less than her Master had done for Peter: to forgive and reconcile. The denial by the Lord here, then, must fall only on those persist in their obstinacy and never repent. It is a terrible thing to hear from the Lord, “Amen, I say to you, I do not know you” (Matt 25:12).