A couple comes home from a church service that was so bad they can't do anything but sleep. The speaker and his wife spend most of the afternoon dozing side by side, and the last line gives the nap a strange purpose: they are "preparing for ash."
That phrase does a lot in four short lines. Ash suggests Ash Wednesday, when foreheads are marked as a reminder of mortality, but it also points to death, cremation, and the title's "end of days." The poem seems to say that the service failed to give them anything meaningful, while the afternoon sleep comes closer to the real message. Sleep is a small rehearsal for dying.
The mood is quiet, wry, and oddly tender. The speaker is a little irreverent about church, yet he isn't bitter. There is comfort in the shared rest, and the humor sits right beside a calm acceptance that everything ends.