The title gives away the poem's central feeling: the speaker is complicit, caught up in violence without having pulled a trigger. The opening greeting to "the gun of a martyr" is strange and unsettling, a respectful or even tender salutation to a weapon. Meanwhile the speaker hears "each reed cry out," as if the natural world is voicing a pain that the speaker won't answer.
Instead, the speaker stays quiet, "as a house in war," a good image of something that has to keep still and hidden to survive, or that has been emptied out. That silence feels less like peace than like fear, or shame.
The last lines turn inward. Hunting for "a better moon / to lie to" suggests the speaker needs some gentler, more forgiving witness to hear a comforting falsehood. The mood is hushed, uneasy, and quietly guilty, a portrait of someone who sees what is happening and can't bring themselves to speak honestly about it.