The Talmudic tractate Berakhot 22a states that either pouring or immersion could be used to purify a ba'al qeri. Just after this Talmudic discussion we are told of one of the most important principles of the Rabbis when interpreting the Torah, that of making a fence or wall to protect the Torah.
In other words, Rabbinic legislation was often concerned with enacting more difficult rulings which would attempt to guard Israel from the sin of breaking the Torah.
R. Hannina specifically said concerning the eventual requirement of immersion in the mikveh in place of dashing water for purification that "they made a useful fence here." Though either pouring or immersion had been equally sufficient, later Rabbinical tradition opted for the more strict practice, making a fence, to keep Israel from falling lightly into sin.
Pirkei Avot, Sayings of the Fathers, commands this restrictive legislation.
"Moses received the Torah from Sinai and transmitted it to Joshua, Joshua to the Elders, the Elders to the Prophets, and the Prophets transmitted it to the men of the Great Assembly. They said three things; Be deliberate in judgment; develop many disciples; and make a fence for the Torah."
"Making a fence for the Torah" means the Sages are to "Surround it with cautionary rules that shall, like a danger signal, halt a man before he gets within breaking distance of the Divine statute itself." Sayings Of The Fathers, by Hugo Bergman, p 13.
We are also told,
"These 'fences' were intended as a precautionary measure against the possible violation of the Torah generally: 'Make a fence for the Law' was already a guiding principle with the men of the Great Synagogue and a leading characteristic of their contribution to the evolution of Jewish religious life.
The 'fences' were meant also to preserve some particular aspect of Law, such as the precepts relating to family purity, and thereby reached down to the very roots of Jewish life. Fences were further raised by Rabbinic authorities to restore the breaches in the Law already made; 'Rab (3rd c.) found an unguarded field and fenced it in' [i.e. he found people transgressing the Law in ignorance and instituted preventative regulations]. The Parables And Similes Of The Rabbis, by R. Dr. A. Feldman, pp 35, 36.
After the Babylonian captivity Rabbinic decisions on purification made the fence of additional laws higher and higher. By late second Temple days there were specific requirements for the dimensions of the pit, and the quality of water to make the mikveh valid.
The requirement for immersion was also part of the fence of the mikveh since a less specific word, rahatz, wash, was regularly used in commands for purification in the Torah.
Modern archaeology has discovered many mikveh pits in Israel which date to late second Temple days and conform to the requirements of Jewish tradition. A number have been found near the Temple and would have been used by Messiah and His disciples when they went up to worship there.
Other mikveh pits have been found at the sights of early Judean Jewish communities of disciples of Yeshua. This indicates the Jewish disciples of Messiah did immerse for purification, but it does not prove the Messianic baptism was by immersion. They would have used these mikveh pools just as the rest of the Jewish people used them, for purification from Torah defilements.
Such evidence proves Israel's wide acceptance of the traditions of the mikveh and its requirement of immersion. It would be perfectly reasonable to believe they also accepted other traditions of purification of that time, including the sprinkling of water for entrance into the Kingdom, as is seen in Kiddushin 72b.
Furthermore, the apostle Paul, who was a Pharisee, was well aware of this Rabbinic attitude of a fence. He wrote that the purpose of the entire Torah was to guard Israel and separate that nation from the world, but Messiah's sacrifice was so great as to break down the dividing wall of the "fence," Ephesians 2:14.
Today multitudes in traditional Christianity mistakenly think they have properly performed a ritual baptism reminiscent of Jewish purification practices. They did not know or follow the intricate laws of the mikveh concerning the water or the pit or the immersion. It is the same with those who pour or sprinkle. For many multitudes their "baptism" did not meet the standard of the first Jewish disciples.
The grievous rifts and contentions between various Christian groups through the ages over the form and significance of water baptism have been a mistaken waste of energy.
Beyond that, if the fence has truly been broken down by Messiah's death then what is the point of such a ritual? Is the Lord going to judge the nations on the basis of having undergone a correct Jewish water baptism? Hardly. His judgment will focus on the purity of heart by the Holy Spirit, not the flesh by water.
Messiah's out-pouring of the Spirit indifferently transcends every denominational dogma about water baptism. Moreover, for many who have undergone this experience, their Spirit baptism occurred years after a water ceremony.
Nevertheless, it is important for Jewish believers to properly perform water rites as testimony to their nation. But ultimately all must recognize, Jew or Greek, that rites cannot satisfy God for salvation. Only faith in Messiah pleases God, "works of righteousness" do not, Titus 3:4-6.