Immersion in the mikvah has offered a gateway to purity ever since the creation of man. Before the revelation at Sinai, all Jews were commanded to immerse themselves in preparation for coming face to face with G-d. Immersion in the mikvah has offered a gateway to purity ever since the creation of man In Temple times, the priests as well as each Jew who wished entry into the House of G-d had first to immerse in a mikvah. On Yom Kippur, the holiest of all days, the High Priest was allowed entrance into the Holy of Holies, If we seek to understand water immersion (baptism in the Greek)
shalom b'SHEM Yah'shua HaMashiach Adonai
as practiced by John the Immerser, we need to understand the
Jewish culture of Mikvah at the time of Yah'shua. Mikvah
The Midrash relates that after being banished from Eden, Adam sat in a river that flowed from the garden.
This was an integral part of his teshuvah (repentance) process, of his attempt at return to his original perfection.
In the desert, the famed "well of Miriam" served as a mikvah. And Aaron and his sons'
induction into the priesthood was marked by immersion in the mikvah.
the innermost chamber of the Temple, into which no other mortal could enter.
This was the zenith of a day that involved an ascending order of services, each of which was preceded by immersion in the mikvah.
from chabad.org