How does knowing that all people are immortals shape how we think of and treat others?
There are no ordinary people. You have never talked to a mere mortal. Nations, cultures, arts, civilization—these are mortal, and their life is to ours as the life of a gnat. But it is immortals whom we joke with, work with, marry, snub, and exploit—immortal horrors or everlasting splendours. This does not mean that we are to be perpetually solemn. We must play. But our merriment must be of that kind (and it is, in fact, the merriest kind) which exists between people who have, from the outset, taken each other seriously—no flippancy, no superiority, no presumption. And our charity must be a real and costly love, with deep feeling for the sins in spite of which we love the sinner—no mere tolerance or indulgence which parodies love as flippancy parodies merriment. Next to the Blessed Sacrament itself, your neighbour is the holiest object presented to your senses. If he is your Christian neighbour he is holy in almost the same way, for in him also Christ vere latitat—the glorifier and the glorified, Glory Himself, is truly hidden. – C. S. Lewis, The Weight of Glory (PDF)
Referenced in Dr. Gregg Strawbridge’s Sermon, February 11, 2018, The Transfiguration (Mark 9:2-9)