In "Composer," the speaker describes a quiet kind of devotion to music. The first lines set up a cycle: water goes back to water, as if everything in nature eventually returns to where it came from, and the speaker goes "to song" in the same way. Music feels less like a choice than a natural pull, like a stream running downhill.
The second stanza states the speaker's creed plainly: living for music is "enough." There's no complaint or longing for more, just the ear "in ecstasy," a body part given over entirely to pleasure. The last lines widen the view. The whole imaginable world is "made of alterations," meaning variations, changes, shifts. A composer hears this as how music works, theme turning into variation, and the poem suggests the world works the same way.
The mood is calm, content, and quietly joyful. The short lines and spare wording feel like a settled breath rather than a loud declaration.