He was crushed with the weight of guilt. After the resurrection of Christ, Jesus had breakfast one day with His disciples. At that time, Jesus talked to Peter. Guilt vanished but Peter never forgot what it meant to receive mercy. Max Lucado comments on Peter's story with these powerful words.
Guilt is th e nerve-ending of the heart.
It yanks us back when we are too near the fire. Please note, there are two fires in Peter's story. The first is the fire of denial, but the second is the fire of discovery. At the first fire, Peter denied Jesus. At the second, Peter confessed him.