Peter turned and saw that the disciple whom Jesus loved was following them. (This was the one who had leaned back against Jesus at the supper and had said, “Lord, who is going to betray you?”) When Peter saw him, he asked, “Lord, what about him?” Jesus answered, “If I want him to remain alive until I return; what is that to you? You must follow me.” John 21.21-22
Peter had just been informed about his future by the Lord. I’m sure he wasn’t pleased with what he heard, so he thought he would ask Christ about what would happen to John. However, Jesus let Peter know that he didn’t need to be concern about the future of John. Peter needed to be focus on his own life
So why should you be concerned about someone else? You best be concern about yourself and where you will be spending eternality. For if you don’t have yourself in a good relationship with God, there is no way you can be of help to anyone else.