Luke 22:34

Now Peter although earnest in spirit, yet still weak in bodily inclination, is declared about to deny his Lord; for he could not equal the constancy of the Divine will. Our Lord's Passion has rivals, but no equal.

(de Con. Ev. l. iii. c. 2.) Now what is here said concerning the foregoing denial of Peter is contained in all the Evangelists, but they do not all happen to relate it upon the same occasion in the discourse. Matthew and Mark subjoin it after our Lord had departed from the house where He had eaten the Passover, but Luke and John before He went out from thence. But we may easily understand either that the two former used these words, recapitulating them, or the two others anticipating them: only it rather moves us, that not only the words but even the sentences of our Lord, in which Peter being troubled used that boast of dying either for or with our Lord, are given so differently, as rather to compel us to believe that he thrice uttered his boast at different parts of our Lord's discourse, and that he was thrice answered by our Lord, that before the cock crowed he should deny Him thrice.

Now the Lord, seeing that Peter spoke boastfully, reveals the nature of his temptation, namely, that he would deny Him; I tell thee, Peter, the cock shall not crow this day, before that thou thrice deny, &c. From hence we draw a great doctrine, that human resolve is not sufficient without the Divine support. For Peter with all his zeal, nevertheless when forsaken of God was overthrown by the enemy.

(in Reg. Brev. ad int. 8.) We must know then, that God sometimes allows the rash to receive a fall, as a remedy to previous self-confidence. But although the rash man seems to have committed the same offence with other men, there is no slight difference. For the one has sinned by reason of certain secret assaults and almost against his will, but the others, having no care either for themselves or God, knowing no distinction between sin and virtuous actions. For the rash needing some assistance, in regard to this very thing in which he has sinned ought to suffer reproof. But the others, having destroyed all the good of their soul, must be afflicted, warned, rebuked, or made subject to punishment, until they acknowledge that God is a just Judge, and tremble.