The speaker seems to be caught between joy and solemnity. The title, "Divinity school," sets up a religious frame, and the opening lines play with it: pleasure becomes something holy, and the speaker forgets they are "water," perhaps meaning something fluid and changeable, not fixed or rigid. Then comes a odd turn. The ache is "devout," and the speaker ends up preaching against smiling, as if they have borrowed the stern tone of a sermon even while enjoying something deeply.
In the second stanza the speaker settles into acceptance. They "own" both sadness and mirth, refusing to pick one over the other. What they can't forget is a passion described as "soft as any night," a gentle, quiet image that cools the preacherly heat of the first half. The mood is reflective and a little wry: tender, slightly contradictory, and at peace with holding opposite feelings at once.