This poem's theme revolves around the power of rain and nature to heal loss and heartbreak. The speaker of Rain on the Roof finds themselves troubled at night by an over-exhausted mind. This is reflected in the oppressive humidity of the weather outside. However, the gentle and familiar sound of rain falling on the roof of their cottage has the power to ease this exhaustion. It brings to mind pleasant memories and recollections that distract the speaker from their daily worries.

Specifically, the sound of rain on the roof brings back pleasant and blissful memories of the speaker's mother and siblings, who the reader can assume are no longer living. Comparing his sister to a seraph and brother to a cherub clue the reader to the speaker's fondness for his lost siblings who are now among the angels. Then the rain reminds the speaker of a lover, long gone. When they hear the rain, these people are no longer absent but present in the speaker's mind as they seem to visit the bedroom.

Pathetic fallacy and the power of nature to imitate the mood of people is central to the theme of this poem. The rain and the darkness of a cloudy night sky seem to mirror the speaker's melancholy mood at first. Soon these negative feelings give way to wistful remembrances as the pleasant sound of the rain above causes them to recall fond memories of togetherness rather than bitter feelings of loss.