The expression is used by Jesus.
John 3:1 There was a man of the Pharisees, named Nicodemus, a ruler of the Jews: 2 The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: for no man can do these miracles that thou doest, except God be with him. 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. 7 Marvel not that I said unto thee, Ye must be born again. 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.
Born again of water
To be born of water refers to immersion in water for the remission of past sins.
Matthew 3:13 Then cometh Jesus from Galilee to Jordan unto John, to be baptized of him. 14 But John forbad him, saying, I have need to be baptized of thee, and comest thou to me? 15 And Jesus answering said unto him, Suffer it to be so now: for thus it becometh us to fulfil all righteousness.
Although Jesus had no sins to be remitted, he insisted on being baptised to show that baptism is necessary for all believers.
Mark 16:15… Go ye into all the world, and preach the gospel to every creature.16 He that believeth and is baptized shall be saved…
Acts 22:16 And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.
1 Peter 3:21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
In baptism, we die with Christ in symbol, and rise out of the waters to begin a new life in Christ.
Romans 6:4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.
Born again of the spirit
God has a spirit and man has a spirit.
1 Corinthians 2:11 For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God.
A spirit is not a separate entity; it is descriptive of the way we think and behave.
In Christ, we must change the way we think to the way God thinks.
This is done by understanding and obeying the word of God.
Romans 12:2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
Ephesians 4:23 And be renewed in the spirit of your mind;
Jesus spoke the words of God.
John 6:63 It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.
It is by the action of the word of God within us that we are born again of the spirit, as Peter describes:
1 Peter 1:23 Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever.
This rebirth cannot be seen outwardly as it takes place inwardly.
It should however become apparent by the way that we speak and act.
Matthew 5:16 Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven.
We must subdue our own will, and do the will of God.
Matthew 7:21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
The will of God has been revealed by Jesus Christ.
Luke 9:35 And there came a voice out of the cloud, saying, This is my beloved Son: hear him.
Believers are to live by the commandments of Christ.
Luke 6:46 And why call ye me, Lord, Lord, and do not the things which I say? 47 Whosoever cometh to me, and heareth my sayings, and doeth them, I will shew you to whom he is like: 48 He is like a man which built an house, and digged deep, and laid the foundation on a rock: and when the flood arose, the stream beat vehemently upon that house, and could not shake it: for it was founded upon a rock. 49 But he that heareth, and doeth not, is like a man that without a foundation built an house upon the earth; against which the stream did beat vehemently, and immediately it fell; and the ruin of that house was great.
I hope you find this helpful.