John 13:38, commentary and pictures

On the night before His suffering Jesus answered Peter's confident promise to lay down his life for Him with the sorrowful prediction that that very night before dawn, before the cock crew, he would deny Him three times. The prediction revealed divine foreknowledge of Peter's heart and hidden weakness which he himself did not know. It was fulfilled when Peter, recognized as a follower, angrily said he did not know Him and the cock crew immediately afterward, dishonoring and deserting Jesus in His humiliation. He could not follow Jesus then, but after his conversion and remorse his pledge was truly fulfilled when he died for the Master he loved, asking to be crucified with his head downward. The verse warns that sincere resolve mixed with self-confidence, self-love and careless exposure to temptation cannot withstand trial, and calls for self-distrust and deeper reliance on Christ, who compassionately warned, did not abandon His disciples, and would have kept Peter watchful and loyal if he had humbly asked for help.

Christ's Prediction of Denial

At the table on the night before His suffering, as He prepared to leave His disciples, Jesus answered Peter's confident promise to lay down his life for Him and to face prison or death with Him. He gave a precise, sorrowful prediction that that very night before dawn, before the cock crew, Peter would deny Him three times. The prediction revealed divine foreknowledge and how accurately Jesus knew Peter's heart and hidden weakness when Peter himself did not know it.

The first denial fulfilled the words when Peter, recognized as a follower, angrily said he did not know Him and the cock crew immediately afterward. It was a cowardly denial that dishonored Jesus and deserted Him in His humiliation.

Peter could not follow Jesus then, but would follow Him later. After his conversion and to his shame turned to remorse, his pledge was truly fulfilled when he did die for the Master he loved before his persecutors, asking to be crucified with his head downward. Even in the manner of his death he followed his Lord afterwards.

Warning Against Self-Confidence

The verse lays bare the contrast between Peter's resolve and the trial he was about to face, for his confident promise to die for Jesus was answered by the prediction that he would deny Him three times before the cock crowed. Peter meant his promise, yet his misplaced confidence, self-love, and hidden weakness left him unprepared for temptation. Under trial he revealed weakness, careless exposure to temptation, and an unsanctified temper instead of reflecting Christ's character.
His careless exposure to those making false and degrading claims about Christ helped lead him to deny his Master. The verse therefore warns of the danger of trusting in one's own strength and resolve, since self-confidence does not make a person able to withstand temptation. Confidence in one's own resolve cannot withstand temptation without reliance and faith.
The warning called Peter to examine his heart, distrust himself, and rely more deeply on Christ. He would have honored Christ by trusting the warning, admitting that he did not know himself, and asking for help to avoid denying Him. Faith in Christ was to safeguard the disciples when the prediction of the three denials before the cock crowed troubled them in the hour of trial.
If Peter had humbly asked, Christ would have saved him from himself, sought the Father's help for him, kept him watchful against temptation, and enabled him to remain loyal when others denied the Lord. Jesus warned His disciples compassionately, did not abandon them in their trial, and assured them that after His resurrection they would be forgiven and remain dear to Him. After denying Him under pressure, Peter remembered the words with deep remorse and was converted.
The words also rebuke self-assured, defiling, unkind talk and passing judgment that hurts souls and spoils God's work as handling strange fire. Those who do so need the Holy Spirit to cleanse away that defilement and place the living coal upon their lips so their counsels are a savor of life unto life and not a savor of death unto death.