John 21:23

Then went this saying abroad among the brethren
It not being rightly understood by some one or more of the disciples present: it was divulged with a wrong sense annexed to it among other persons; who, though not of the eleven, yet were followers of Christ, children of God, that belonged to the same family, and were, in a spiritual relation, brethren to each other, and to the apostles:

that that disciple should not die;
but should remain till the second coming of Christ, and be found among them that shall be then alive, and be changed. And such a notion not only was among the ancients; but Beza, in his notes on this text, tells us of a strolling wicked fellow, that gave out that he was the Apostle John; and was encouraged by some, particularly Postellus, a Sorbonic doctor, but was afterwards burnt at Tholouse.

Yet Jesus said not unto him he shall not die, but if I will that he
tarry till I come, what is that to thee?
These are the words of John himself, the disciple spoken of, who gives a true and just account of Christ's words, freeing them from the false sense that was put upon them; which shows his ingenuous disposition, his integrity and love of truth; being unwilling that such an error should obtain among the disciples, and pass in the world for truth.