Peter asked Jesus the above question shortly after Jesus explained to Peter how he would die. Like many today Peter wonder how someone else would do. Jesus' answer to Peter was threefold. "Jesus saith unto him, If l will that he tarry till I come, what is that to thee? follow thou me' (John 21:22).
The three parts are:
(1) If I will that he tarry till I come,
(2) What is that to thee?
(3) Follow thou me.
Jesus first told Peter, "Do my will. Peter, do what I want you to do, because my will is the will of the Father (John 6:38-39). If we are doing the will of God, then knowing that others are doing His will should be enough for us without knowing all the details.
Second, Jesus asked Peter, "What is that to thee?" Jesus wanted Peter to understand that each and every disciple (Christian) has a work to do. Paul, in I Corinthians 12:25-27, wrote of the different things that different members of the body of Christ have to do.
Third, we must follow Jesus if we are wanting to receive eternal life (John 1:35-39). Will you follow Jesus?