The ceremony consisted of procession, chants, sacrifice, prayer, and sometimes a sacred meal. Magic and masquerade, tableaux and dramatic representations might be part of the procession. In most cases the basic ritual was prescribed by custom, and every movement of it, every word of the hymns and prayers, was preserved in a book kept sacred by the family or the state; rarely was any syllable or action altered, or any rhythm; the god might not like or comprehend the novelty. The living speech changed, the ritual speech remained as before; in time the worshipers ceased to understand the words they used, but the thrill of antiquity supplied the place of understanding. Often the ceremony outlasted even the memory of the cause that had prompted it; then new myths were invented to explain its establishment: the myth or creed might change, but not the ritual.
The Story of Civilization II, The Life of Greece, by Will Durant, page 193