The speaker of "Sinner" seems to be returning to a dark place, one where rage and desire live out of sight. The opening word "again" suggests this isn't the first visit; the howling is something the speaker keeps coming back to. The second stanza is vaguer. It talks about a "touch of absence" and a strange act that "would never have been," as if the speaker is half-admitting that something happened, or failed to happen, and can't quite name it.
The turn comes in the last stanza. The speaker says they insist on a "fall," choosing to see their failing as a descent rather than denying it. The reason is a surprise: down in the pit they met "my brother owl." An owl is a creature of night and hidden things, and calling it a brother makes the darkness feel less lonely. The mood is shadowy and confessional, but it ends with a strange comfort. The speaker doesn't seem to regret the fall, because it led to company and a kind of kinship with the wild, nocturnal side of themselves.