A couple make love in the night, and the morning after, the speaker is still caught up in it. The poem compresses that into a few quiet lines. "Fell into a music" suggests the two of them slipping into something bigger than themselves, a harmony that happened to them rather than something they planned. "Rose singing to rose" is a lovely knot of meaning: they get out of bed, and the repeated word also hints at flowers, or at two people lifting toward each other.
Then the scene jumps to the office, an ordinary, daytime place. The speaker can hardly eat even "a bit of bread," the plainest food there is. That's the surprise of the ending. Hunger has been displaced by something else, and the whole day feels shaped by the memory of the night.
The mood is tender, giddy, and a little dazed. The speaker isn't boasting or explaining. He's simply full, in a way food can't touch, and the poem's brevity makes that feeling seem both private and very easy to recognize.