That he tarry - That he live. The same word is used to express life in Phi 1:24-25; 1 Corinthians 15:6.
Till I come - Some have supposed this to refer to the destruction of Jerusalem; others to the day of judgment; others to signify that he would not die a violent death; but the plain meaning is, “If I will that he should not die at all, it is nothing to thee.” In this way the apostles evidently understood it, and hence raised a report that he would not die. It is remarkable that John was the last of the apostles; that he lived to nearly the close of the first century, and then died a peaceful death at Ephesus, being the only one, as is supposed, of the apostles who did not suffer martyrdom. The testimony of antiquity is clear on this point; and though there have been many idle conjectures about this passage and about the fate of John, yet no fact of history is better attested than that John died and was buried at Ephesus.
What is that to thee? - From this passage we learn:
1.That our main business is to follow the Lord Jesus Christ.
2.That there are many subjects of religion on which a vain and impertinent curiosity is exercised. All such curiosity Jesus here reproves.
3.That Jesus will take care of all his true disciples, and that we should not be unduly solicitous about them.
4.That we should go forward to whatever he calls us to persecution or death - not envying the lot of any other man, and anxious only to do the will of God.