"Slow dance" feels like a quiet, slightly nervous moment between two people who are close but still figuring each other out. The opening lines are almost comically small and self-conscious: is my knee red, which hand is handsome. The speaker seems to be noticing bodies in pieces, a knee here, a hand there, the way you do when you're shy or newly intimate and can't quite take in the whole person.
Then the poem settles. "Alone with each other" is a lovely turn, suggesting privacy that isn't lonely. Learning to dance becomes a way of learning one another, step by step. The last lines move toward something almost spiritual: two people praying, yet being one is holy. The poem seems to wonder whether closeness is a kind of devotion, even as the two stay separate. The mood is tender, hushed, and a little playful, with awkwardness slowly giving way to reverence.