The speaker describes something that comes and goes like a daily visitor, leaving each morning and returning at night. The title, "Warmth," suggests what it might be, though the poem never says outright. Judging by the imagery, it could be a feeling of comfort, joy, or emotional connection, something that rises and falls with light and dark.
At first the tone is almost casual. The visitor is sometimes welcome, sometimes not, and the speaker seems to accept this uneven rhythm. But the poem slowly darkens. When "darkness beckons," the thing takes the speaker's soul with it, and the absences stretch from a night to a day, a week, a year. The short lines near the end feel like time dragging on.
The last line, "It wasn't coming back," lands flatly and without drama, which makes it hit harder. The mood moves from quiet familiarity to loss and numbness. The playful, borrowed title adds a bitter irony, as if the speaker is waving off something that has already gone for good.