Now Peter was sitting out in the courtyard, and a servant girl came to him. “You also were with Jesus of Galilee,” she said. But he denied it before them all. “I don’t know what you’re talking about,” he said. Then he went out to the gateway, where another servant girl saw him and said to the people there, “This fellow was with Jesus of Nazareth.”He denied it again, with an oath: “I don’t know the man!”After a little while, those standing there went up to Peter and said, “Surely you are one of them; your accent gives you away.”Then he began to call down curses, and he swore to them, “I don’t know the man!” Immediately a rooster crowed. Then Peter remembered the word Jesus had spoken: “Before the rooster crows, you will disown me three times.” And he went outside and wept bitterly. – Matthew 26:69–75
John Calvin says Peter’s rash vow to remain with the Lord (Matt. 26:33) and subsequent failure encourage us not to rely on our own weakness, but to earnestly rely on the Spirit. It is easy to say that we will never deny the Lord. But our flesh is weak, and we should not think ourselves strong apart from the strength He alone can give us. We have all denied Him in some way; let us therefore lean on His Spirit that we may never do so again.