John 3
3 Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God.
4 Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born?
5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
OT saints were born again. Being born again isn't a new thing.
Joh 3:7
Marvel not that I said unto thee, Ye must be born again.
Joh 3:8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.
Joh 3:9 Nicodemus answered and said unto him, How can these things be?
Joh 3:10 Jesus answered and said unto him,
Art thou a master of Israel, and knowest not these things?
The implication is that being born again was not a new teaching and "masters" of OT scripture should have known this already. That means being born again is found in the OT:
1Sa 10:6 And
the Spirit of the LORD will come upon thee, and thou shalt prophesy with them,
and shalt be turned into another man.
1Sa 10:7 And let it be, when these signs are come unto thee, that thou do as occasion serve thee; for God is with thee.
1Sa 10:8 And thou shalt go down before me to Gilgal; and, behold, I will come down unto thee, to offer burnt offerings, and to sacrifice sacrifices of peace offerings: seven days shalt thou tarry, till I come to thee, and shew thee what thou shalt do.
1Sa 10:9 And it was so, that when he had turned his back to go from Samuel,
God gave him another heart: and all those signs came to pass that day.
Eze_18:31 Cast away from you all your transgressions, whereby ye have transgressed; and make you
a new heart and a new spirit: for why will ye die, O house of Israel?
Is being another man and having another heart (new man and new heart) after receiving the Holy Spirit the same as being born again? I say yes!
2Co_5:17 Therefore if any man be in Christ,
he is a new creature: old things are passed away; behold, all things are become new.
Eph_4:24 And that ye put on
the new man, which after God is created in righteousness and true holiness.
Also, this is how one could inherit eternal life before the new covenant came into effect:
Mat 19:16 And, behold, one came and said unto him, Good Master,
what good thing shall I do, that I may have eternal life?
Mat 19:17 And he said unto him, Why callest thou me good? there is none good but one, that is, God:
but if thou wilt enter into life, keep the commandments.
Mat 19:18 He saith unto him,
Which? Jesus said,
Thou shalt do no murder, Thou shalt not commit adultery, Thou shalt not steal, Thou shalt not bear false witness,
Mat 19:19 Honour thy father and thy mother: and, Thou shalt love thy neighbour as thyself.
Luk 10:25 And, behold, a certain lawyer stood up, and tempted him, saying,
Master, what shall I do to inherit eternal life?
Luk 10:26 He said unto him, What is written in the law? how readest thou?
Luk 10:27 And he answering said, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy strength, and with all thy mind; and thy neighbour as thyself.
Luk 10:28 And he said unto him,
Thou hast answered right: this do, and thou shalt live.
The concept of regeneration is well known in the OT. Anyone that knows the bible knows that this is true:
Joh 3:7 Marvel not that I said unto thee, Ye must be born again.
Joh 3:8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.
Joh 3:9
Nicodemus answered and said unto him, How can these things be?
Joh 3:10 Jesus answered and said unto him,
Art thou a master of Israel, and knowest not these things?
Barnes:
John 3:10
A master of Israel - A “teacher” of Israel; the same word that in the second verse is translated “teacher.”
As such a teacher he ought to have understood this doctrine. It was not new,” but was clearly taught in the Old Testament. See particularly Psa_51:10, Psa_51:16-17; Eze_11:19; Eze_36:26. It may seem surprising that a man whose business it was to teach the people should be a stranger to so plain and important a doctrine
Psa 51:10
Create in me a clean heart, O God; and
renew a right spirit within me.
Psa 51:11 Cast me not away from thy presence; and
take not thy holy spirit from me.
Eze 11:19 And I will give them one heart, and
I will put a new spirit within you; and I will take the stony heart out of their flesh, and will give them an heart of flesh:
Eze 36:26
A new heart also will I give you, and
a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh.