The speaker begins with something unsettling: a morning in which they hear "the prisoners / that are to die." It's left vague. We don't know who these prisoners are or whether the speaker hears them literally or in some imagined way, but the line sets a heavy tone straight away.
The second stanza turns to a purchase. The speaker pays for a picture so heavy they can't decide what to do with it. The picture seems to stand for more than an object: perhaps an image of suffering, or a burden taken on that can't easily be put down or displayed. The final stanza admits a fear, that the speaker has a "natural aptness" for any cross, an easy readiness to take on suffering. The title, "Kenosis," a word for self-emptying, fits this idea of giving oneself up.
The mood is quiet, wary and sombre. The short lines and plain statements make the confession feel honest rather than dramatic.