Written as a billet-doux, a love letter, the poem tells a small, sad story in four short stanzas. Someone writes a letter that looks loving but is built on deceit. The pen moves "senselessly," the page is only half full, and yet the words on it are "bold" and false. They speak "silently," which is a neat contradiction: the letter makes noise inside the reader's head without making a sound.
The woman who receives it believes every word. Her heart beats blissfully, and the word "insanely" hints that her trust is a little reckless. In the last stanza, the writer is called a "martyr," but the poem seems to treat that word ironically. He dies "open-eyed" and "bravely" arranges his own retreat, so the letter may be a cowardly way of leaving dressed up as sacrifice.
The speaker stays at a distance and simply reports. The mood is quiet, ironic and sorrowful, helped by the repeated "-eat" rhymes (sheet, deceit, beat, retreat), which close each stanza like a door.