We all know that Peter was the first pope. What we often forget is that Peter was also a terrible sinner. I can think of at least five times in the Gospels where Peter messed up; but the time that he denied Jesus was the absolute worst.

St. Matthew tells us that it was a maid who first approached Peter in the courtyard. The maid recognized Peter as a friend of Jesus, but Peter denied knowing him. Then, another girl—not a woman, but a girl—saw Peter and said, “This man was with Jesus the Nazarene.” Again, Peter denied it. The third time St. Matthew tells us that it was some bystanders who recognized Peter as a friend of Jesus by his speech. And once more, Peter denied knowing Jesus.

That’s about as bad as it gets. Just when your best friend needs you most, you deny even knowing him. And it’s not as if those questioning him were all that intimidating—a maid, a girl, and a group of bystanders—people who wouldn’t seem to be much of a threat to a future pope. And Peter knew it. St. Matthew tells us that upon the cock’s crow, “Peter went out and began to weep bitterly” (Matt. 26:75). Earlier that night, Peter promised Jesus that his faith would never be shaken, but there it was, a crumbled mess. And there he was, the one who Jesus had handpicked to be the fearless leader of the Apostles, off in the corner weeping.

Of course we know that there is more to the story. After Jesus suffers, dies, and rises from the dead, he has another encounter with Peter. This time it’s on the shore of the Sea of Galilee, where St. John tells us that Jesus invites the disciples to breakfast. It’s also the place where Jesus asks Peter if he loves him—three times. Three times Peter responds that he loves Jesus, and in doing so, Peter experiences Jesus’ love, forgiveness, healing, and mercy. Jesus makes all things new, and in that moment, he makes Peter new too.

But a question remains. How in the world can Peter ever forget that terrible moment in the courtyard when he committed the worst of sins by denying that he even knew Jesus? Surely if we know about his terrible and cowardly act two thousand years later, people also knew well about it back then. And I’m sure that some even reminded him of it from time to time, saying, “Come on man, you’re the coward who denied even knowing Jesus, and now you’re telling me that I should believe in him? Please.” How in the world did Peter ever forget his terrible sin and move forward?

Here’s the truth: Peter never forgot the fact that he denied Jesus. That cowardly act was something that he could never take back. What’s done is done. Peter couldn’t go back in time and make things right again. So what happened? How did Peter do it? How did the worst coward turn into one of the most courageous men in Christianity, eventually requesting to be crucified upside down because he thought himself unworthy to die in the same manner as his Lord Jesus?

What happened to Peter was that although he knew he was a great sinner, he also knew that Jesus loved him completely, as he was—a sinner. To paraphrase St. John Vianney, Peter knew that his sins were but a grain of sand in the ocean of God’s great mercy. It was the merciful love of Jesus that re-created Peter and made him new. Peter couldn’t do anything about his sins other than confess them. But Jesus could; and he did. Peter denied Jesus three times, so in his love, Jesus offered Peter an opportunity to tell Jesus that he loved him—three times. And with that Peter was forgiven and made new. From that point on, whenever Peter thought back about the time he denied Jesus, he didn’t think about it as sin committed, but sin confessed and forgiven.

One of the greatest lessons that Peter teaches us is how to deal with past sin, especially if it’s something big, nasty, and outright embarrassing. The devil’s great trick is to make us think that God couldn’t possibly forgive certain sins, because they’re just too severe. Even if we’ve confessed certain sins, and in our heads we know that God is merciful and has forgiven us, sometimes just thinking back to those embarrassing moments makes us doubt the power of God’s mercy and the fact that he can really make all things new. But Peter’s story reminds us that those kinds of thoughts are from the Evil One. God is not a liar and he truly does make all things new for those who accept his merciful love.

When Peter looked back and thought about that time he denied Jesus, or the time he couldn’t walk on water, or the time Jesus told him, “Get behind me Satan,” he looked back on those sins not as sins committed, but as sins confessed and forgiven. When we sin, we need to admit it and ask for the Lord’s forgiveness. As Pope Francis likes to say, “The Lord never tires of forgiving.” But once our sins are forgiven, we have to remember them precisely as that—as sins forgiven.

One reason that Peter was so credible and remains so credible to this very day is that we can all somehow relate to his story. He screwed up, and he screwed up bad. There was nothing he could do to fix himself except throw himself at the mercy of Jesus, which is exactly what he did. Jesus forgave his sin, and from that point on, Peter looked back at those dark moments as bright ones, not because of anything that he did, but because of what the Lord did for him. Peter experienced a healing of memory. He no longer remembered his sins as sins committed, but as sins confessed and forgiven. It made all the difference in the world. And it still does.