Peter, in his sermon in Acts 3, talks about how the people of Jerusalem had denied Christ before Pilate and denied Christ to get Barabbas.
Peter twice used the word denied.
He knew something about denying Christ before another. He knew something about denying Christ so that a guilty party could go free (in his case, he himself). Yep. He knew something about denying Christ.
And yet he brings it up. Why use that kind of language? If Peter were a politician, he would be skewered by social media, late night comedians, and attack ads. But he's not a politician. He's an apostle. And his best (and only) defense against denying Christ was that Christ had forgiven his betrayal.
End of story. Drop the mic. Exit stage right.
Peter's greatest failure became a platform for his proclamation.
May it be so for us too.