Jesus restored Peter after he’d denied Jesus three times and told him to feed His sheep. Then He told Peter what sort of death he would have to glorify God. (According to Christian tradition Peter was crucified in Rome under Emperor Nero Augustus Caesar)
In verse 20 Peter, turning around, saw the disciple whom Jesus loved following and He said, “But Lord, what about this man?”
Here’s the first mistake Peter made here. We can often make the same mistake. He turned around and looked at another follower of Jesus.
As Christians it can be tempting to look at others and compare our destinies to theirs. Others’ destinies may seem easier and more glamorous, and our own may seem lacking. But Jesus put Peter straight by saying, “If I will that he remain till I come, what is that to you? You follow Me.”
Jesus was essentially saying,” Never mind what I’ve called other people to do. That’s not your concern. You follow Me. Work out your own salvation with fear and trembling. I have a unique purpose and calling for you and for the people you’re comparing yourself to”