The Phil Keagy song is a from Lewis's Poems, which hardly anyone reads.
It's "As the Ruin Falls." I think it was written to reflect on the death of his wife. I once taught an Elderhostle, a class for retired people, on C. S. Lewis (I'm a college professor) and read that poem for them and it profoundly affected two or three of the people there who had lost spouses.
Keagy does a marvelous job on it. The flute-guitar minimalism is wonderful.
David W. Landrum
(also a guitarist)