Then Peter came up and said to him, "Lord, how often will my brother sin against me, and I forgive him? As many as seven times?" Jesus said to him, "I do not say to you seven times, but seventy-seven times.
Peter did not seem to think that he was in danger of falling into sin; his question was, How often should I forgive my brother? But very soon we hear that Peter has fallen. I can imagine that when he did fall, the sweet thought came to him of what the Master had said. The voice of sin may be loud, but the voice of forgiveness is louder.
Taken from the book Day by Day with DL Moody DL Moody 1837-1899