John 13:37

The blessed Peter, as we have just heard, is ordered to follow. And yet he had originally been thinking of going ahead when he said to the Lord, "I will lay down my life for you." He was so sure of himself that he was unaware of his fear. He wanted to go ahead of the one he should be following. It was a good thing he was eager to do, but he did not keep to the right order.

When he had shaken off the dread of being the traitor, and was shown to be one of His own, he afterwards asked boldly himself, while the others held their peace. "What sayest thou, Peter? He said, 'thou canst not,' and thou sayest, 'I can'? Therefore thou shalt know from this temptation that thy love is nothing without the presence of the impulse from above." Whence it is clear that in care for him He allowed even that fall. He desired indeed to teach him even by the first words, but when he continued in his vehemence, He did not indeed throw or force him into the denial, but left him alone, that he might learn his own weakness.

Peter promised he would die for him, and he was not even able to die with him. He had staked more, you see, than his credit could stand. He had promised more than he could fulfill, because it was in fact unfitting that he should do what he had promised. "I will lay down my life," he said, "for you." But that is what the Lord was going to do for the servant, not the servant for the Lord. So as he had staked more than he was worth, he was then loving in an inverted sort of way; that is why he was afraid and denied Christ. Later on, though, the Lord, after he has risen, teaches Peter how to love. While he was loving in the wrong way, he collapsed under the weight of Christ's passion. But when he was loving in the right way, Christ promises him a passion of his own.