Had Christianity never existed, the time of the Roman Empire still would have been one of the most consequential and transformative periods in the history of religion. Romans across the empire formed a cult around their quasi-divine emperor, and the emperor was only one of the many subjects of worship outside of the traditional pantheon. Roman religion and philosophy became increasingly blended, and the Roman Empire also saw the rise of the mystery cults aiming toward salvation in the afterlife.
Polytheism (meaning “many gods”) was the original religion of most near-Eastern civilizations; Judea was a prominent exception. The Greeks and Romans believed in the existence of many immortal gods who existed within time and within the space of the cosmos. The Greeks worshipped Zeus, whom the Romans knew as Jupiter. He was the most powerful god, the ruler of the cosmos. The term “pantheon” refers to all the gods, but Zeus and eleven others were the most powerful.
The polytheistic Greeks and Romans also worshipped numberless gods and spirits of nature, particularly the facets of nature connected with human life and prosperity. Worshippers sought to maintain peace with the gods and secure the blessings of fertility – in agriculture and marriage – through prayer and sacrifice. The necessity of the gods’ blessing was a major factor behind the Romans’ persecution of Christians. Christians refused to worship the Roman gods and thus deflected the blessings or even brought curses upon those around them.
The philosophy of Plato also came to play a key role in Greco-Roman polytheism. According to Platonism, a single, transcendent God existed, and humans possessed souls that survived beyond the death of the body. Platonism gradually pervaded Roman religion and experienced a revival during the 2nd and 3rd centuries.
While philosophy and religion became increasingly intertwined, the Roman Empire also saw a massive growth of mystery religions, which were separate from the public religious system. These groups or cults taught secretive rituals. Their members sought eternal life through initiation into the inner circle and participation in “mysteries,” the cult’s rituals.
The Eleusinian mystery cult gained a large following. The followers of this religion worshipped Demeter and Persephone, believing that Persephone’s descent into and resurgence from the underworld was an allegory for death and eternal life. From outside of the traditional pantheon came the Egyptian goddess Isis, who found many adherents among the Romans. Isis’ followers believed that she was the queen of heaven and that every year her tears flooded the Nile River and watered the crops. Her husband, Osiris, was the god of death. When Seth, the god of chaos, murdered Osiris, Iris resurrected him long enough to conceive a son named Horus. This myth of life, death, and rebirth was the foundation of Isis’ mystery religion.
The most complete, detailed surviving expression of polytheism and Isis worship and belief is The Golden Ass, a novel written by Apuleius, an Isis follower and Platonist in North Africa, during the second century. The Golden Ass is the first complete Latin novel to survive from the ancient world. It combines comedy, religion, social realism, and folklore into an allegory of religious devotion. The novel reflects Apuleius’ belief that Isis was the source of redemption and salvation.
The story of The Golden Ass is told by Lucius, a bright and insatiably curious young man whose curiosity gets the best of him and results in his transformation into an ass. In ass form he passes through the hands of many owners and undergoes many trials. At one point he is forced to work in a mill, turning round and round; this is a metaphor for the soul in the eternal grind.
The Golden Ass is a framework story. The longest story within the main one is the tale of Cupid and Psyche, an enduring story that has been retold throughout the ages and depicted in art. In this story a young woman named Psyche, whose beauty is matchless, draws the attention of the jealous goddess Venus – and Venus’ son Cupid, who is lovestruck. He disobeys his mother and takes Psyche to be his bride, and they live together happily, but Cupid cannot reveal his identity to her and thus only comes to her at night. One night, when her husband has fallen asleep next to her, Psyche is curious and lights an oil lamp. While she is struck by Cupid’s beauty, a drop of oil spills from the lamp and lands on his shoulder. He is startled awake and flies away in a hurry. Venus gives Psyche a series of impossible labors to complete, and during the last, she is beset by an infernal sleep. Cupid cannot bear to live without her, so he revives her and brings her to Olympus, where she drinks a cup of ambrosia and becomes immortal. At last, Cupid and Psyche are perpetually united in marriage. The story of Cupid and Psyche deals with the topics of death, rebirth, suffering, and redemption and acts as a metaphor for eternal life—claiming that the soul – the psyche – must be united with pure love to attain eternal life.
After this story within the main story, Lucius’ adventures continue. At the end of The Golden Ass, Lucius lays down on a beach, exhausted, humiliated, and still an ass. There he prays,
“O by whatever name, and by whatever rites, and in whatever form, it is permitted to invoke you, come now and succor me in the hour of my calamity… Remove me from the hateful shape of a beast, and restore me to the sight of those that love me. Restore me to Lucius, my lost self.” 
While he lays on the beach, a goddess rises from the water and comes to him. She responds:
“Moved by your prayer I come to you… – I, whose single godhead is venerated all over the earth under manifold forms, varying rites, and changing names… Some call me Juno. Some call me Bellona. Some call me Hecate. Some call me Rhamnusia. But those who are enlightened… call me by my true name, Queen Isis.”
Evidence of Platonism and mystery religions are evident here. Lucius’ many adventures are a metaphor for the idea that the human soul is a divine element imprisoned in the physical body.
The Golden Ass and the mystery religion in it can help the reader understand Christianity because Christianity, in a way, is a mystery religion. Christianity’s initiates must be catechized in doctrine and receive the sacrament of baptism before participating in the Eucharist, the central sacrament or mystery. Redemption is a major theme of both belief in Isis’ cult and Christianity, as Christians’ belief that Christ buys humanity out of sin and death.
 Trans. Jack Lindsay (Indiana UP, 1962), 236.