Leviticus 14:1-9 Ceremonial washings are as old as the Torah itself. God commanded the Hebrew people to wash their clothing before he gave them the law at Mount Sinai (Exodus 19:10). In Leviticus 8 and 16, Aharon and his sons were commanded to wash before they ministered in the Tabernacle, and there were ritual cleansings for various flows of body fluids (Lev 15). Perhaps the most instructional passage in the Torah about the act of total immersion (t’vilah) is the healing of leprosy.
The practice of mikveh (the ritual bath where t’vilah was performed) was quite common in the second temple period, as shown by a large number of references to this custom in the Talmud. The ritual immersions for healing and service continued as prescribed by the Torah. With the destruction of the Temple, the custom of mikveh also changed. The priests’ cleansings and the related healings were no longer practical, though modern Judaism maintains the need for mikveh in some situations.
The Bible says little about the actual construction of a mikveh. However, what the Bible leaves undefined, the rabbis have elucidated in great detail. Despite all the details, one should not lose sight of the mikveh’s meaning. The Bible distinguishes between the holy and the profane. The waters of the Mikveh teach the Jewish people a great deal concerning these truths. One Jewish interpretation of the mikveh relates it to an experience of death and resurrection, and also to the re-entry into the womb and re-emergence. Immersed fully, one is like the foetus in the womb, and coming up out of the water, it is as if one is reborn. The individual who has sinned and become impure is transformed; he dies and is resurrected and becomes a new creation, like a new-born child (Buxbaum 569). The most prominent example of total immersion in the New Testament is found in John 1. Yochanan the immerser (John the Baptist) was a prophet who practiced it as an integral part of his ministry. This account matches many of the details already known about the mikveh of that day and its significance in Jewish culture.
the High Holy Days, which include the Jewish New Year (Rosh-HaShanah) and the Day of Atonement (Yom Kippur), is the most focused time of the year when Isra’el assesses her spiritual condition and turns back to God. To this day, men still immerse in the mikveh as a sign of their inward cleansing as they spiritually prepare for the Holy Days.
Jewish Customs -CJB pp 147.