The title makes the fire a preacher, a "homilist," and its message is bleak: humans are made for destruction, a kind of growth or blemish on the earth rather than part of it. The poem doesn't say what fire this is, so it can be read as a literal blaze, a wildfire perhaps, or as a more general image of ruin and the guilt we feel about it.
What stands out is the speaker's response. He doesn't argue or panic. He calls it "a dull sermon" and simply goes home. That flat reaction can feel like weary indifference, or like a refusal to accept the fire's grim verdict. Either way, the tone is quiet and dry.
The ending shifts the mood. The "cold little house / full of night" is small, plain, and lonely. After the huge talk of destruction, the speaker is left with a modest human space and the dark. It suggests that grand pronouncements matter less than the chill of ordinary life, though the poem leaves us unsure whether that is comforting or sad.