Long before Christianity the Eleusinians instituted the ritual of baptism as part of initiation into the mystery. The initiates were required to undergo a preparatory purification; they marched in a procession to the sea and washed their sins away by baptism. The Roman historian Livy (64/59 BCE to 17 CE) mentions that ceremonial washing preceded initiation into the mysteries of Dionysus. Through baptism they secured glorious immortality in the afterlife. Their message was "new life grows out of every grave."
For the Eleusinians being born again and securing forgiveness of sins by submersion in water was a mystery. Baptism symbolized the purification of the soul. Tertullian wrote, "... in the Apollinarian and Eleusinian rites they are baptized, and they imagine that the result of this baptism is rebirth and the remission of the penalties of sins ..."
The mystery religion ritual of baptism was adopted first by the Essenes and then by the Christians. The Essenes borrowed the ritual of baptizing either from the Eleusinians or the Pythagoreans. During their initiation they made a covenant with God, which included baptizing and repentance. The Manual of Discipline (a.k.a. Rule of the Community) required sincere repentance before baptism and entering the covenant. (1QS 5:13-14) "Those [candidates] will not enter into the water [of baptism] ... for they are not purified except they repent from their wickedness." The Manual describes the procedure of entering the covenant. (1QS 3:8-9, 12 ) "... through the submission of his soul to all God's ordinances ... he may purify himself with the water-for-impurity and sanctify himself with rippling water ... this will become for him a covenant of eternal Communion [with God]."
Ritual purification with water was part of early Judaism. For the most part it involved ceremonially washing the hands, while in a few instances it required washing the whole body. It was done to remove uncleanness after touching something unclean, such as a corpse. There are distinct differences between the Hebrew rituals and the Essene rituals of baptism. The Hebrews washed their bodies whereas the Essenes practiced total immersion. The Damascus Document forbade baptism in bodies of water insufficient for immersion. The Hebrews did not perform such ritual for those who entered Judaism whereas the Essenes did. Sometime during the first century CE proselyte baptism was introduce to Judaism.
The Essenes and John the Baptist practiced baptism before the early Christians. John was in many ways was an Essene. He lived like the Essenes of Qumran and preached similarly. Mark indicates that he did not baptize "in the name of Jesus Christ." John was not a Christian, yet Mark implies that the sins of his converts were forgiven. (Mark 1:4) John did baptize in the wilderness, and preach the baptism of repentance for the remission [forgiveness] of sins. (KJV) Josephus, too, wrote that John the Baptist urged the Jews to baptize for the remission of sins and the purification of the soul. Baptism for the forgiveness of sins was an established practice before Jesus. The early Christians borrowed baptism from John the Baptist.
Like the mystery followers, early Christians conducted baptizing at the time of initiation. Peter ordered baptizing as soon as they repented. (Acts 2:38) Then Peter said to them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins ... (KJV)
Christianity was a continuation of pre-existing beliefs. As we will further examine, it was created by the fusion of Judaic and Greek beliefs. Such syncretism was common during that era. Religions were put together using elements of other religions. All mystery religions shared common beliefs. People were not offended by such inter-borrowing. The mystery religions were not competing with one another. They got along harmoniously. People belonged to several mystery religions simultaneously. Only Christianity prohibited its converts from belonging to other religions. This was not a problem in the beginning. However, when Christians grew in numbers (in the second century CE) the other religions became offended by Christianity's competitiveness and its lack of sharing. As a result, they started persecuting the Christians.
From Andrew Benson's book The Origins of Christianity and the Bible.
I do not agree with everything he says but there is some interesting history there.
[Edited on 3-5-2004 by Visigoth]