"10,000 people could do a better job than you!" Sr. Briege McKenna told a gathering of priests. "But that’s beside the point. God chose you." No priests are perfect, in other words, but God calls them to service anyway. This was true for St. Peter, as we see in today’s gospel. Jesus chose Peter as his chief shepherd, the first pope. At the same time, he acknowledges Peter’s weaknesses.
The three times Jesus asked Peter to affirm his love recalls Peter’s three denials during Jesus’ trial. The first two times, as originally written in Greek, Jesus asked Peter if he gave him "agape" - sacrificial love. In response, Peter answered that he gave him "phileo" - brotherly love. So in his third question, Jesus asked Peter not for "agape" love, but brotherly love. And Peter said he could.
Peter knew that he wasn’t yet capable of "agape," and Jesus knew it too. But Jesus also knew that one day Peter would be. That’s why he said that Peter himself would die on a cross.
Jesus doesn’t wait until we’re perfect to call us to service, either. Instead, he meets us where we are, and gives us grace to grow. Jesus knows that we’re broken sinners. Yet still he loves us, and uses us to build up his kingdom. Jesus doesn’t call the qualified. He qualifies the called.