"Now Peter was sitting outside in the courtyard. And a servant girl came up to him and said, "You also were with Jesus the Galilean." But he denied it before them all, saying, "I do not know what you mean."
And when he went out to the entrance, another servant girl saw him, and she said to the bystanders, "This man was with Jesus of Nazareth." And again he denied it with an oath: "I do not know the man."
After a little while the bystanders came up and said to Peter, "Certainly you too are one of them, for your accent betrays you." Then he began to invoke a curse on himself and to swear, "I do not know the man." And immediately the rooster crowed. And Peter remembered the saying of Jesus, "Before the rooster crows, you will deny me three times." And he went out and wept bitterly." Matthew 26:69-75 ESV
What changed Peter from a man who would deny Christ to a waiter and a servant girl into a man who would die crucified upside down who would not even imagine any kind of denial. Record has it he chose to die upside down because he didn't feel worthy to die in the same way his Savior died.
What does that to a man?
Grace does. Grace expressed in a thousand different ways over many years. Grace, Grace and more Grace.
Regret would have killed Peter. Grace saved Peter. Grace Loved Peter. Love transformed Peter.
So it is with us.