In just a few lines, the poem pictures a church that has been burned down, leaving only ash. The speaker doesn't tell us who set the fire or why. Instead, the focus falls on the aftermath: a place once meant for worship now filled with something dead and grey. Calling the church "melancholy" is interesting, because it makes the building itself seem sad, as if the fire left it grieving rather than simply destroyed.
The rain then arrives and becomes the "poor sermon." A sermon usually fills a church with words and meaning, but here the only voice left is weather, and a feeble one. The word "poor" can suggest both inadequate and pitiable. The title, "Kenosis," is a word associated with emptying, and the poem seems to match it: the building is emptied of its purpose, its people, and its words. The mood is quiet, bleak, and still, though there is a faint hint that the rain might offer some kind of comfort, however slight.