All religions borrow from the traditions that came before them, and Christianity is no exception. Since Christianity was based on the teachings of a Jewish healer and its earlest members were primarily Jews, it’s no surprise that much of its structure, tradition, and scripture derives from Judaism. The Christian Old Testament is essentially the Hebrew Bible, and even the most influential early translation of that Bible, the Greek Septuagint, was the work of over 70 Jewish scholars translating from the original Hebrew. The Sabbath and feast-days, the singing of Psalms and hymns, choral music, the use of candles and incense, of an altar with a tabernacle and an altar lamp, the “sacrifice” of the mass and the eucharist, are rooted in Judaic practices going back to the Temple days, as are the role of the priest and of special vestments to be worn during services. The structure of Jewish clerical authority with its high-priest became the basis for the Christian hierarchy of priests, bishops, and cardinals, headed by the pope. Even the word “Amen” is Hebrew, usually translated as “so be it,” although it actually means “truly.”
The other major influence on the developing Christian church was a mystery religion that probably originated in Persia from in much earlier Zoroastrian beliefs. Mithraism takes its name from Mithra, an ancient Iranian god of heavenly light, similar to the Aryan Mitra; when the religion was adopted by the Romans, the name became Mithras. The Greeks called this and similar cults — like those of Eleusis, Dionysus, and Isis — mysteria, from a root meaning “to keep one’s mouth shut.” The “mystery” religions in general demanded absolute secrecy, under pain of death, in exchnage for initiation into rites capable of transforming one spritiually and psychologically. This is one reason we know so little about the Mithraic mysteries, the other reason being that nearly all memory of them was eradicated by the victorious Christians.
Images of Mithras survive, however, in underground temples from England to Asia Minor, showing the deity as a handsome youth kneeling on a bull while stabbing it with his knife. Some scholars associate this figure with the personification of the constellation Perseus, hypothesizing that the cult arose in response to the realization that the reign of Taurus as the constellation of the spring equinox had been replaced by that of Pisces. The Mithraic cult proved especially popular among Roman bureaucrats, legionaires, and slaves, who celebrated it in grottoes and underground chapels. And it appears to have influenced many aspects of Christian belief and practice. According to attacks on Mithraism by Christian authors, its members celebrated sacraments such as baptism and the eucharist, marked their foreheads with a cross, and believed in Mithras as their savior, redeemer, and final judge. Sunday had always been the holy day of the Mithraists, who also celebrated December 25 as the birthday of the sun, in reassurance that the days had begun to grow longer following the winter solstice.