Early Jewish rabbis spoke of proselytes — gentiles converting to Judaism — as being “reborn.” Encyclopedia Judaica states, “A proselyte terminates all former family ties upon conversion and ‘is considered a newly born child’ ” (volume 13, page 1184, article “Proselytes”).
The Interpreter’s Dictionary of the Bible states:
The Jewish direction for developing theologically such an illustration as Jesus provided is evident in the somewhat similar rabbinic comparison of the new proselyte with a newborn child… “I make you a new creature, like a woman who is pregnant and gives birth” (Rabbi Judah bar Simon). (volume 4, page 27, article “Regeneration”)
Further discussion of these concepts is found under the subject “Baptism” in Hastings’ Dictionary of the Bible and in chapter 6 of The Life and Times of Jesus the Messiah, by Alfred Edersheim. A summary of these points is also given in the Theological Dictionary of the New Testament, 1985 one-volume edition, pages 114-115, under the heading “gennao.”
New birth, as a figure of speech, is known to refer to proselyte conversion. It was understood to mean conversion of the mind and heart, beginning a new spiritual life with a new way of thinking, leaving one’s old ways and ideas completely behind.
The Life and Times of Jesus the Messiah, by Alfred Edersheim: “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. The expression, therefore, was not only common, but, so to speak, fluid.”
The Talmud says, “A man who became a proselyte is like a child newly born.”
According to Jamieson, Fausset and Brown: “The Jews were accustomed to say of a heathen proselyte, on his public admission into the Jewish faith by baptism, that he was a new-born child. But our Lord here extends the necessity of the new birth to Jew and Gentile alike—to everyone.”
The Soncino Talmud states: “As your forefathers entered into the Covenant only by circumcision, immersion and the sprinkling of the blood, so shall they (the proselytes) enter the Covenant only by circumcision, immersion, and sprinkling of the blood” (Keritot 9a).
According to Adam Clarke’s commentary, “[The Jews] held that the Gentile who became a proselyte was like a child newborn.”
The figure of speech ‘born again’ was not foreign to Nicodemus. It was a figure applied to a bridegroom on the occasion of his marriage, to the Chief of the Academy on his promotion, to the king on his enthronement, and to the proselyte on his entrance into Judaism. 72 The application of this expression to the entrance of a Jew into the kingdom of God left Nicodemus’ head reeling. (Alfred Edersheim, The Life and Times of Jesus the Messiah Grand Rapids: Eerdmans, 1965, I, p. 384.)
Edersheim, in his “Life and Times of Jesus the Messiah”, mentions a number of circumstances to which this applied. Proselytes to Judaism were considered newly born. So too were the bridegroom in his marriage, the Chief of the Academy on his promotion and the king on his enthronement. It was a term used to describe a new beginning in an important circumstance of life, where the person took a new role as a beginner, like a child, having to start at the bottom and learn a role in life all over again.
The Life and Times of Jesus the Messiah Alfred Edersheim 1883, Book III The Ascent: From The River Jordan To The Mount Of Transfiguration
Chapter 6 The Teacher Come From God And The Teacher From Jerusalem – Jesus And Nicodemus (St. John 3:1-21.)
It has been thought by commentators, that there is 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 16 – was likened to a child just born. 17 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. 18 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 a 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, 19 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.