John Calvin Commentary John 18:25

"Now Simon Peter was standing and warming himself. They said therefore unto him, Art thou also [one] of his disciples? He denied, and said, I am not." — John 18:25 (ASV)

He denied it. How shocking the stupidity of Peter, who, after having denied his Master, not only has no feeling of repentance, but hardens himself by the very indulgence he takes in sinning! If each of them in turn had asked him, he would not have hesitated to deny his Master a thousand times.

Such is the manner in which Satan hurries along wretched men, after having degraded them. We must also consider the circumstance related by the other Evangelists (Matthew 26:74; Mark 14:71), that he began to curse and to swear, saying, that he did not know Christ. Thus it happens to many persons every day.

At first, the fault will not be very great; next, it becomes habitual, and eventually, after conscience has been lulled to sleep, he who has accustomed himself to despise God will think nothing unlawful for him, but will dare to commit the greatest wickedness. There is nothing better for us, therefore, than to be vigilant from the start, that he who is tempted by Satan, while he is still uncorrupted, should not allow himself the smallest indulgence.