It covers ancient mythologies from around the world and their legacies in later religions.
One point that he focuses on is that the word "myth" has a much more significant meaning than what we usually give it when we dismiss something as mere "myth" because it is not literally true historically or scientifically.
The meaning of myth is not in literalness, which misses the forest for the trees. Myths express meanings that are significant to the human psyche, which Campbell equates with Jung's collective unconscious, as the basis for religious and psychological symbolism.
Campbell was an ardent believer in diffusion of ideas and mythological symbols from one culture to another and carried from past to present. Some of his examples of diffusion have since been established as incorrect by later anthropological and archaeological studies. But others have shown the origins and continuity of mythologies and symbols pretty well.
For example, he points out that the serpent was a symbol of fertility in the settled agricultural societies of the ancient Middle East. The reason for the snake as a symbol is that it sheds its skin, which "dies" like old crops, but "renews" itself with new skin, as seeds renew plants. Also, the serpent crawls on the earth, turning over soil as if "plowing." So it became a phallic symbol for agricultural societies, which held human fertility ceremonies between temple priests and temple priestesses at the time of planting. In some societies, this also involved human sacrifices.
When the nomadic herder tribes of the Hebrews settled down in Canaan among agricultural people who practiced fertility rites, they found the practices abhorrent because of the public ritualization of sex and the ritual killing of human beings. So, in the Hebrew sacred stories, the serpent is evil and tempts Eve who then "seduces" Adam into sin. Lesson of the story: Don't be like those fertility people.
The Genesis story reflects a Hebrew value system at odds with their neighbors. The prejudice against agricultural societies is again expressed in the story of Cain and Abel. Abel tends flocks and uses one of his animals as a sacrifice to God. But Cain is a farmer who sacrifices plants from his harvest. The story says that Abel's sacrifice was more pleasing to God, so Cain killed Abel out of jealousy. According to the bias in the story against Cain's sacrifice, God has nothing against plants. But he does oppose the practices of agricultural societies in HOW they plant and harvest their crops. A religious expression in mythology of the values and customs of the ancient Israelites, using opposition to symbols and customs that are sacred to their agricultural neighbors.
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