The speaker begins with a plain, happy statement: their body gives them joy. The comparison that follows, to a swan or a fish, suggests ease and grace, the way creatures seem perfectly at home in their own element. There's no shame or struggle here, just pleasure in simply being a body.
The second half moves indoors, into a private room "in the dark." The speaker sings a song or two, and the sound is good. The detail about the bed being out is small but telling: with the furniture gone, the room is emptier, and an empty room lets sound carry and ring. That fits the title, "Resonant," which can describe both a room and a person who feels fully alive in themselves.
The mood is quiet, contented, and intimate. Nothing dramatic happens. The poem simply catches a moment of private satisfaction, where body, voice, and space seem to agree with one another.