The speaker admits that belief doesn't come naturally. They believe in death only because they feel they ought to, and even then just every other day, as if faith were a chore that has to be taken in turns. The tone is dry and a little wry, with the speaker half-shrugging at their own doubts.
Death itself is hard to picture here. The speaker admires its "nothing" and compares it to a plain picture hanging on a wall: quiet, undramatic, something you could pass by without much thought. It isn't frightening so much as blank.
Then the poem turns on "but." What the speaker believes in more steadily is ordinary life: kindness, a bit of conversation, and "a great deal of supper." The humor of that last line is also its warmth. Against the big, empty idea of death, the poem sets small, shared comforts, and the mood settles into something gentle, grounded, and quietly content.