Last week, we witnessed this beautiful moment as Jesus restored Peter from the damage he had done to himself through those three denials. Jesus loved Peter. So, in these following few verses, we see how Jesus assures Peter that he will never deny Him again. In fact, Jesus tells Peter that he would glorify God by dying a martyr's death in old age. Those words that assured him of his faithfulness as a follower of Jesus also brought a grim reality of the kind of death he would suffer. Jesus invited Peter to follow Him. By the time the gospel of John was written, Peter had already suffered a violent death.
However, that day on the beach, while Peter walked and talked with Jesus, those prophetic words brought a bit of envy as he once again took his eyes off Jesus, but this time, he wasn't looking at the storm that nearly caused him to drown, this time he was looking back at the "beloved disciple" with envy and comparison. Jesus' path for Peter was uniquely his, and John's path was likewise. So, Jesus asked, "What is it to you." It was more of a statement than a question. Jesus calls each of us personally and uniquely to follow Him.