20Peter, turning around, saw the disciple whom Jesus loved following them; the one who also had leaned back on His bosom at the supper and said, "Lord, who is the one who betrays You?" 21So Peter seeing him said to Jesus, "Lord, and what about this man?" 22Jesus said to him, "If I want him to remain until I come, what isthat to you? You follow Me!" 23Therefore this saying went out among the brethren that that disciple would not die; yet Jesus did not say to him that he would not die, but only, "If I want him to remain until I come, what is that to you?"
Joh_21:20 "the disciple whom Jesus loved" This refers to the account found in Joh_13:25. Why he is designated in this cryptic manner is uncertain (cf. Joh_13:23; Joh_19:26; Joh_20:2; Joh_21:7; Joh_21:20). Possible theories are
1. traditional Jewish writings of the first century did not mention the author by name
2. John was so young when he became a follower of Jesus
3. John was the only Apostle who stayed with Jesus during the trials and crucifixion
Joh_21:22 "Jesus said to him, 'If I want him to remain until I come, what isthat to you'" This is a third class conditional sentence. We must remember that we are to deal with our own gifts and ministries and not be concerned with what God has planned for others! A possible reason for adding chapter 21 was to answer the misunderstanding over this very issue. Apparently there was an early rumor (possibly Gnostic) that John was to live until the Second Coming (John does speak of the Parousia, cf. 1Jn_3:2).
▣ "follow Me" This almost summarizes the personal invitation of John's Gospel (cf. Joh_1:43; Joh_10:27; Joh_12:26; Joh_21:19; Joh_21:22). This emphasizes the personal aspect of the gospel, while "believe that" emphasizes the content aspect of the gospel.