John 21, 23:

[Rebecca_New]

This passage has befuddled me for so long, and the footnote makes it even more difficult. I have longed for direction with this.

When Peter saw him, he said to Jesus, “Lord, what about him?” Jesus said to him, “What if I want him to remain until I come? What concern is it of yours? You follow me.” So the word spread among the brothers that that desciple would not die. But Jesus had not told him that he would not die, just “What if I want
him to remain until I come? [What concern is it of yours?]”

 

[Thomas_More_1]

This is from the commentary by Fr. Haydock

Ver. 21. Lord, what shall this man do? St. Chrysostom thinks, it was the love and friendship, that St. Peter had for St. John, that moved him to ask this question. (Witham)

Ver. 22. Jesus saith: so I will have him remain,[3] &c. That is, in case I will have him remain; or, as it is in the Greek, if I will have him remain, what is that to thee? It is thy duty, and thy concern, to follow me. (Witham) — When Christ told St. Peter to follow him, he meant, that he should go like himself to the death of the cross; but when he says of St. John, So I will have him to remain till I come, he insinuates that his beloved disciple should not undergo a violent death; but remain in the world, till he should visit him by death, and conduct him to glory. It may likewise be understood of the Revelation, in which our Saviour manifested himself in his glory to this his beloved disciple. In the Greek, it is, if I will have him to remain; and this is the true reading, according to Estius, and Jansenius, bishop of Ghent, authorized by many Latin copies. Others refer these words of Christ to his coming to destroy Jerusalem: an epoch which St. John survived.

Ver. 23. This saying, therefore:[4] that is, a report went about among the disciples, the John was not to die. But St. John himself, as St. Augustine and St. Chrysostom observe, took care to tell us, that Christ said not so. Nor do we find any sufficient grounds to think that St. John is not dead. (Witham)

I’m not sure what the difficulty is you’re having. On the surface, Peter is concerned (by love? by worry?) to know if John will have a similar fate as he. Jesus basically tells him, “don’t worry about him, follow Me.”

 

[Fidelis]

The Navarre Bible Commentary on John says this:

20-23. According to St. Irenaeus (“Against Heresies”, II, 22, 5; III,
3, 4) St. John outlived all the other Apostles, into the reign of
Trajan (98-117 A.D.). Possibly the evangelist wrote these verses to
dispel the idea that he would not die. According to the text, Jesus
does not reply to Peter’s question. The important thing is not to be
curious about what the future will bring but to serve the Lord
faithfully, keeping to the way He has marked out for one.

To quote St. Padre Pio:

“Why should you worry whether God wants you to reach the Heavenly home by way of the desert or by the fields, when by the one as well as by the other one arrives all the same at a Blessed Eternity?”