The Mercy of God
The increase of the enemies’ temptation accumulates with Peter’s sin. When Peter is pressed a second time and with stronger opposition, he comes up with a naked and empty denial, which is in effect an implied confession. In this second denial, to make it more credible, he must make himself more impious and to save face with men, he not only denies but renounces faith in God with oaths and curses. In all of this Christ is witness, not only to his lie, but his open revolt.
How deep the dye of sin and the degree of corruption that faith exists alongside of. Yet that faith, although smothered, was preserved by the prayers of Christ. Had the same action of malice against Christ that Peter displayed come from an unregenerate heart, it would have been the irremediable sin against the Holy Ghost. But this sin in Peter was preceded by fear and weakness, it was the sin of a believing and faithful heart.
In this the Christian learns both to despair of his own strength and not to despair of the mercy of God, which can keep faith in that heart. The mercy of God can raise a man up to martyrdom who had so deeply plunged himself into apostasy. He that suffered Judas to be the subject of His judgement raised Peter from a sin which was in itself as great as Judas’, to be a preacher and witness of His mercy.