Baptism
Craig Keener on Acts 2:37
Peter instructs the people how to call on the Lord’s name (2:21): be baptized in Jesus’ name. Because baptism was a sign of conversion to Judaism normally reserved for pagans, Peter’s demand would offend his Jewish hearers and cost them respectability. He calls for a public, radical testimony of conversion, not a private, non-committal request for salvation with no conditions. “In the name of Jesus Christ” distinguishes this sort of baptism, requiring faith in Christ, from other ancient baptisms; this phrase simply means that the person being baptized confesses Christ. (Acts always uses this phrase “be baptized” - the passive, never the active; presumably it thus does not denote a formula said over the person being baptized, but rather indicates the confession of faith of the person receiving baptism; see 2:21 and 22:16
Messianic Bible on mikvah
A man who wants to become Jewish must undergo the two main requirements: circumcision and immersion. A woman, however, must only be immersed.
When Gentile converts go down into the waters of the mikvah, they leave behind their pagan ways—symbolically dying to their old life—and come up out of the water as a newborn child with an entirely new identity. They are in essence reborn.
So, we see that the term “born again” originated in Judaism.
Understanding that the term “born again” referred to a conversion to Judaism sheds light on the conversation between Yeshua (Jesus) and the sage Nicodemus in the Book of Yochanan (John).
Nicodemus wondered, “How can a man be born when he is old? He cannot enter a second time into his mother’s womb and be born, can he?” (John 3:4)
From his Jewish perspective, Nicodemus essentially asked, “How can I convert to Judaism if I am already a Jew?”
Yeshua answered, “A man must be born of water and spirit.” (John 3:5)
He was explaining to Nicodemus that we cannot rely on our “Jewishness” (or any other heritage) to enter the kingdom of heaven. A conversion of our spiritual condition is necessary for salvation.
In Hebrew, the word mikvah has the same root letters as the word hope! The great Prophet Jeremiah used the word mikvah in the sense of hope:
“O Hashem, the Hope [mikvah] of Israel, all who forsake you will be ashamed … because they have forsaken Hashem, the fountain of living water.” (Jeremiah 17:13)
When Believers are immersed in the waters of the mikvah, as a declaration of faith in Yeshua, they have the hope of a new life, a new beginning in Him.
“For I know the plans I have for you, says the Lord, plans to prosper you and not to harm you, plans to give you a hope [tikvah] and a future.” (Jeremiah 29:11)
It is evident from Yeshua’s final instructions below that tevilah or mikvah would play a part in making all the Gentile nations into Talmidim (disciples) of the Jewish Messiah. He said,
“Go therefore and make disciples of all the nations, immersing them in the name of the Father and of the Son [Yeshua] and of Ruach HaKodesh [Holy Spirit].” (Matthew 28:19)