Ancient religion tended to take the form of festivals or long, multi-part ceremonies that expressed a particular principle, and Christmas is our strongest surviving example. What we now call "Christmas" is immensely old; in its present incarnation it is mostly about our love for our families and especially for our children, and such evidence as we have indicates that it has always been about something in that ballpark. That is certainly what its current deity, Santa Claus, is about. He is not "worshiped" as the old Deities mostly were not, but he is an important part of our lives and his festival is usually the time of our year that we care about most. And he is understood as real and present in exactly the same way that the old Gods were understood as real and present.
Another example of an ancient festival is the Cheyenne Indian ceremony called the Massaum. The Massaum was long and complicated, lasting several days, and each part expressed what the Cheyenne called Thunder and the ancient Greeks called Dionysos. At one point in the Massaum, little plays were acted out. These plays expressed the same principle that Greek tragedy expressed, Dionysos/Thunder, but instead of being based on a historical incident like tragedies were they were based on dreams that someone had or had once had that strongly expressed the power of Thunder.
When we first began to see the form of Greek tragodia from the archaic period it reminds us of a typical ceremony in an African village, with large numbers of masked and costumed dancers, singing and dancing on the hard ground of the market place, to simple melodies and enormously complicated rhythms.
First a bull was sacrificed, then a pig, then the singer/dancers would begin. They would sing of a historical event—historical as the ancient Greeks understood "history." For the ancient Greeks a historical event was not one that affected the way in which large numbers of people were governed and dominated, but one that expressed something of what it is like to be a human being—in this case the side of human beings that the Cheyenne called Thunder and the Greeks called Dionysos. They would sing the song of someone who was torn apart by psychological forces, by some impossible conflict. They would sing to a single figure, he who was being torn, who would be costumed and masked more elaborately than anyone else and who stood alone on a sacrificial altar. The choros would sing, and he who was isolated and torn would answer, and they would sing back and forth until the story was told, and the character played by the man on the altar was torn apart and destroyed. The sacrificial altar may have evolved into a stage, or it may have disappeared and the stage developed later.
Whether later tragedy was performed on a stage or on flat ground, the choros and the singers were now on the same level. The choros shrunk to twelve or fifteen, and the number of singers grew from one to two or three. The conflict was now not between the individual and the choros, but between two individuals or parties, represented by individual singers. The choros was still important musically, but it was no longer an important part of the plot. In the classical period tragedy was one of four types of ceremony, all part of a long festival called the Great Dionysia and all expressing the same basic principle, Dionysos.
Whenever the choros said very much, it sang. The individuals sang, spoke rhythmically as the characters do in Shakespear’s plays, or they did something in between— and all singing was accompanied by an instrument. We have numerous descriptions of the modes the music was in, we know the characteristics of the instruments, and we have descriptions of the various dances the choros did. The purpose of the tragedies was to express the principle the Greeks called, Dionysos, and the information we have of tragic music and dance make it clear that they were musically just as Dionysian as their purpose would imply, that they were dominated by rhythm, and that Janis Joplin would have felt much more at home singing in them than would someone with the Victorian conception of what "the classics" should be about.