C.S. Lewis preached this sermon in Oxford in 1942. I appreciate many aspects of it.
1. Perspective on modernity.
He distinguishes Kantian from Biblical ethics. Desiring your own good is all right with God, as that leads to His glory. Desire isn't the problem, as many moderns and Stoics tend to think. Misplaced desire is the problem. We fool about with paltry things when pleasures forevermore await at God's right hand (Ps 16). We hope for a future we can barely imagine, like Latin grammar students who will one day enjoy Virgil, but can't see in the grammar stage what it could be good for. Modernity tries to convince us that this world is all there is. Lewis wants to cast a spell to break that enchantment. There is a glory outside ourselves and outside this wold to which our desire and this world point us.
2. Humble honesty.
When faced with the puzzling or repellent parts of Christian revelation in the Bible, Lewis doesn't flinch, evade or make euphemisms. He calls them repellent - a very impious thing to do! He admits there must be something there he needs. His thoughts are not the ultimate criteria of truth. He sees that modernity has trained him to not be drawn naturally to thrones or robes, and works to understand glory through other Christian writers. He is quick to recognize and reject false humility and self-posturing as hindrances to true piety.
3. Biblically corrected psychology.
By this I don't mean counseling or adopting Freudianism. Rather, he helpfully analyzes his own emotions and how they affect his thoughts about God. Part of the glory of heaven is receiving approval from God. "Well done, good and faithful servant." And part of us (wrongly) retreats from this in false humility or an over-developed worm theology that says that heaven could never be "about us." Well, no, but God did go to the trouble of making and redeeming you for a reason.
In the end, God's countenance confers glory or shame. We stand outside or inside of glory. We haven't yet got in - we are this side of immortality, not that side. Lewis is a clear, black-and-white thinker in this way.
5. Coram Deo.
C.S. Lewis senses the presence of God. It weights heavily on him. When we stand before God, we will be inspected, and might even survive it! The ultimate glory is being known by God. Without using the pious jargon, he gets at that uncomfortable feeling of being convicted, purified, corrected, in God's presence.
This is a very under-appreciated aspect of Lewis, not often thought of in connection with children's stories, or academic essays (his standard writing fare). But there are many lessons in his stories (not preachy, though), and much in his abstractions to affect our actions. The surprise ending of this sermon is that we deal with immortals in our neighbor, with many of whom we will spend eternity. This should influence our relationships, our merriment, our charity, even our politics (during WWII!).
We shouldn't give glory to any but God alone.
But we can thank God for giving gifts to the church (Eph 4:11), in teachers and story tellers like Clive Staples Lewis.