Myths of Greece and Rome, by Jane Harrison, [1928], at sacred-texts.com
Dionysos had absorbed into his personality two non-Hellenic divinities--(1) a god of wine, orgy, and ecstasy from Thrace, (2) a Cretan mystery god, Zagreus, who is substantially one with the Egyptian god of immortality, Osiris.
As to his origin, though his name means, undoubtedly, "young Zeus," Dionysos is essentially the son of his mother, Semele; later he is affiliated to Zeus by a rebirth.
[paragraph continues] Semele is just the Thracian form of the earth-goddess. "Zemlya" is Slavonic for "earth." We have the word in Nova Zembla (New Earth or Land). The whole worship of Dionysos is matriarchal, of the mother as well as of the son, the mother sometimes appearing as nurse. So Sophocles:
The Bacchantes are the mothers; they tend the young of wild things, and they have magical power to make the whole world break into blossom.
At the great ritual of the mothers all Creation stirs anew.
No wonder Dionysos and his mother did not find easy access to a patriarchal Olympus!
The worship of Dionysos has one characteristic that distinguishes him from the other gods, and is of special interest in helping us to understand the making of a god. Dionysos is always accompanied by a worshipping band, a thiasos. His worshipping band are the Satyrs, his mother's are the Mænads. None of the other gods have a thiasos. The reason is clear, once the psychology
of the band is realized. Dionysos is the god of ecstasy, but it is ecstasy of the group, not the individual. Euripides said of the Bacchic initiate: "His soul is congregationalized." We have seen, notably in the case of Poseidon, that all the Olympians are projections of the desires, imaginations, of the worshipper; but only in the case of Dionysos do we catch the god at the moment when the ecstasy of the group projects him. This is no fancy. Plato preserves for us an Orphic text: "Many are the wand-bearers, few are the Bacchoi"; that is, many perform the rite of Bacchus, few become, or, as we should say, project, the god himself.
By becoming one with the god he had projected, the worshipper of Dionysos attained immortality. That is the doctrine of each and every mystery religion. No one sought to become Zeus or Athene or Apollo. That would have seemed folly and insolence. "Strive not thou to become a god," says Pindar; "the things of mortals best become mortality."
It is probable that all Greek gods were originally accompanied by a thiasos, and were projected by their worshippers. But most of the Olympians have long passed this stage. Their worship is not an ecstasy; it is a sober service of sacrifice, prayer, and praise. God and man are eternally sundered.
Another trait marks Dionysos off from the Olympians. They are wholly human; he keeps about him some vestiges of plant and animal shape. He is tree-god (dendrîtes), and at will he can change himself back into plant or animal form. When the Bacchantes in extreme peril call upon Dionysos for vengeance, his ancient incarnations loom in upon their maddened minds:
[paragraph continues] The mystery gods represent the supreme golden moment of Greek mythology. They are caught, fettered for an instant in lovely human shapes; but they are life-spirits barely held; they shift and change. Dionysos is a human youth, lovely with curled hair, but in a moment he is a wild bull and a burning flame. The beauty and the thrill of it!