What are the motifs in The Long Dark Tea-time of the Soul by Douglas Adams?

Ancient Principles in a Modern World is a recurring idea. The old gods are in a most distressing situation. They were created in ancient times by Norsemen, who wanted their deities to be immortal. The gods are not designed to die, even when all their worshipers do. The gods all get confused by modern society and technology and basically just live as homeless people. Sometimes they can die, but it takes a special effort. Most mortals do not even see the gods, as though they are invisible. There are two ways to deal with this conflict.