From a treatise on John by Saint Augustine, bishop

“The Church recognizes two kinds of life as having been commended to her by God. One is a life of faith, the other a life of vision; one is a life passed on pilgrimage in time, the other in a dwelling place in eternity; one is a life of toil, the other of repose; one is spent on the road, the other in our homeland; one is active, involving labor, the other contemplative, the reward of labor.

“The first kind of life is symbolized by the apostle Peter, the second by John. All of the first life is lived in this world, and it will come to an end with this world. The second life will be imperfect till the end of this world, but it will have no end in the next world. And so Christ says to Peter: Follow me; but of John he says: If I wish him to remain until I come, what is that to you? Your duty is to follow me.“

(Augustine, Tract. 124, 5, 7: CCL 36, 685-687)