John Chrysostom — as excerpted in the Catena Aurea on Matthew 26:30-35

“[I suppose also that Peter fell into these words through ambition and boastfulness. And they had disputed at supper which of them should be greatest, whence we see that the love of empty glory disturbed them much. And so to deliver him from such passions, Christ withdrew His aid from him. Moreover observe how after the resurrection, taught by his fall he speaks to Christ more humbly, and does not any more resist His words. All this his fall wrought for him; for before he had attributed all to himself, when he ought rather to have said, I will not deny Thee if Thou succour me with Thy aid. But afterwards he shews that every thing is to be ascribed to God; Why look ye so earnestly upon us, as though by our own power and holiness we had made this man to walk?]q (Act 3:12.) Hence then we learn the great doctrine, that man’s wish is not enough, unless he enjoys Divine support.”