In addition to being circumcised (if male) a proselyte to Judaism also underwent a mikveh. He ceremonially "died" as a Gentile as he went under the water, and was "born again" as a Jew when he came out.
Sound familiar?
Nicodemus (probably aka Rabbi Nakdimon ben Gurion) was not being dense when he said, "How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?" (John 3:4). He was asking, in a very rabbinic way (and with the question-phrasing of a student asking his master--that is, he was showing Yeshua the utmost respect), "I'm already Jewish. Should I be literally 'born again' then? Or are you using the phrase in a different way?"
Well, the information seems to be accurate as far as it goes, which is more that can be said for the source quoted by XeniaSt.
I'm still trying to figure out how all those folks got immersed out in the wilderness of Sinai.
He ceremonially "died" as a Gentile as he went under the water, and was "born again" as a Jew when he came out.
But we are not talking about conversions to Judaism. There were apparently many aspects of the mikveh that have no relationship to the baptismal rites of the Christian church.
"I'm already Jewish. Should I be literally 'born again' then? Or are you using the phrase in a different way?"
That a curious way of putting it, and of course there is nothing in the text to suggest that's what he was thinking. Baptism is not even mentioned, only physical birth (born of water) and spiritual birth (born of the Spirit).
The term "born again" or "born anew" seems to be somewhat fluid, according to Edersheim:
And yet, though Christ never descended to the standpoint of Nicodemus, we must bear in mind what his views as a Jew would be, if we would understand the interview. Jesus took him straight to whence alone that 'Kingdom' could be seen. 'Except a man be born from above, he cannot see the Kingdom of God.' It has been thought by commentators, that there is here an allusion to a Jewish mode of expression in regard to proselytes, who were viewed as 'new-born.' But in that case Nicodemus would have understood it, and answered differently - or, rather, not expressed his utter inability to understand it. It is indeed, true that a Gentile on becoming a proselyte - though not, as has been suggested, an ordinary penitent - was likened to a child just born.. It is also true, that persons in certain circumstances - the bridegroom on his marriage, the Chief of the Academy on his promotion, the king on his enthronement - were likened to those newly born. The expression, therefore, was not only common, but, so to speak, fluid; only, both it and what it implied must be rightly understood. In the first place, it was only a simile, and never meant to convey a real regeneration ('as a child'). So far as proselytes were concerned, it meant that, having entered into a new relation to God, they also entered into new relationship to man, just as if they had at that moment been newly born. All the old relations had ceased - a man's father, brother, mother, sister were no longer his nearest of kin: he was a new and another man. Then, secondly, it implied a new state, when all a man's past was past, and his sins forgiven him as belonging to that past. It will now be perceived, how impossible it was for Nicodemus to understand the teaching of Jesus, and yet how all-important to him was that teaching. For, even if he could have imagined that Jesus pointed to repentance, as that which would give him the figurative standing of 'born from above,' or even 'born anew,' it would not have helped him. For, first, this second birth was only a simile. Secondly, according to the Jewish view, this second birth was the consequence of having taken upon oneself 'the Kingdom;' not, as Jesus put it, the cause and condition of it. The proselyte had taken upon himself 'the Kingdom,' and therefore he was 'born' anew, while Jesus put it that he must be born again in order to see the Kingdom of God. Lastly, it was 'a birth from above' to which reference was made. Judaism could understand a new relationship towards God and man, and even the forgiveness of sins. But it had no conception of a moral renovation, a spiritual birth, as the initial condition for reformation, far less as that for seeing the Kingdom of God. And it was because it had no idea of such 'birth from above,' of its reality or even possibility, that Judaism could not be the Kingdom of God.Life and Times of Jesus the Messiah