Imagining an afterlife, the speaker keeps things modest and earthy. Instead of heaven, they picture coming back as a bear, and the idea seems to appeal to them: "great satisfaction" is a surprisingly warm phrase for such a plain, animal existence. But they don't push the fantasy too hard. "In the meantime," sunlight and "the old ground" are enough, so contentment is already available here and now.
The last stanza turns a little sharp. The angels are "ridiculous," and all they can see is "a book," which suggests a rigid, official version of the afterlife, perhaps one made of doctrine and text rather than living things. The speaker seems to find that view narrow and slightly silly.
The mood is quiet, wry, and settled. There's no fear of death here, just a gentle preference for the physical world, its warmth and soil, over anything abstract.