John 18:17

St. John gives here Peter's first denial, which is reunited to the other two by all the preceding evangelists. This is one of the circumstances, which the others may have neglected, to unite three similar facts, and relating to the same object. (Bible de Vence) --- St. Peter, the prince and head of the Church, was permitted to fall, to teach him to treat with more mildness and condescension those, whom he would afterwards have to raise out of the same miserable state of sin. One weak and frail man is placed over another, that seeing him unhappily fallen, he may give him his kind and helping hand, to free him from that unhappy state, in which he knows himself to have been. (St. John Chrysostom) --- Of all which our divine Saviour suffered in the court of Caiphas, nothing so much affected him as the dangerous fall of Peter, the chief of all his apostles, who had received the most signal favours from him. He had boasted that very night, that although all the rest of the disciples should abandon their master, he would never forsake him. Yet, see the weakness and inconstancy of human nature; at the voice of a poor maid, he forthwith denies his master; repeats his denial a second, and a third time, and even swears with an imprecation, that he never knew the man. O what is man, when he confides too much in himself! Let us look to ourselves, and see, that we never fall into the same unfortunate state. But if we have the misfortune to imitate this apostle in his fall, let us likewise imitate him in his speedy repentance: for immediately after his fall, going out, he wept bitterly; a practice which, it is said, he ever after retained, as often as he heard the cock crow. (Butler's Lives of the Saints)