Nicodemus was one of the Pharisees, who were Jewish religious leaders who were very conservative and in some cases very legalistic but who had a reverence for God and His Word the Holy Bible (then just the Old Testament). When it is stated that Nicodemus was a ruler of the Jews it could mean he was a member of the Jewish governing council the Sanhedrin that included leading Pharisees of Israel. He came to Jesus by night because Jesus was quite controversial including urging the Jews to rethink the way they regarded God, His salvation and His word and so Nicodemus at first didn't want to be seen talking with Jesus but he respected him enough to hear some of his teaching. Jesus knew that keeping and honouring the law and reverence for God weren't problems with Nicodemus so he got right to the point by saying he needed a new birth and new nature by the Holy Spirit instead of self effort by the works of the law. Jesus could also be trying to relate to Nicodemus and his idea that God was with Jesus because of the miracles he did by then referring to new birth of the Holy Spirit and the Kingdom of God which were the agents by which Jesus did his miracles and part of the way God was with him because he was teaching in his words and works of the Kingdom of God.
When Jesus said except a man be born again he cannot see the kingdom of God he meant a man or person has to not just be born physically initially but also needs to be born a second time spiritually by the Holy Spirit to see or understand or discern the kingdom of God and its spiritual realities in the spirit realm and the spiritual aspect of God's word the Holy Bible etc. Nicodemus misunderstood what Jesus meant and thought instead of a second different spiritual birth Jesus was talking about a second physical birth. Although there are different interpretations of what water in water and the spirit means I personally think especially from the context of the next verse that water here means the water associated with the first physical birth or birth of the flesh. The part about spirit would be the second birth or to be born again and would be by the Holy Spirit or Spirit of God. This spiritual birth after the physical birth enables a person to enter the kingdom of God or gain citizenship or membership in the Kingdom of God and at present to come before God's presence in Heaven spiritually in prayer in the new nature in Jesus' name. When the born again believer or Christian dies we will enter the Kingdom of God on a more permanent basis with our spirit or true selves in the born again version and at the rapture we will enter the kingdom of God with our spiritual bodies. Then Jesus says that that which is born of the flesh is flesh and that which is born of the spirit is spirit meaning if we are not or not yet born again or born of the spirit we only have a fleshly nature that is under God's condemnation. On the other hand if we are born again or born of the spirit we have a second spiritual nature that we can have a preserved identity for us fit for dwelling in heaven with God and Jesus forever. This is a work of the Holy Spirit. The idea is that for born again Christians or believers our fleshly natures will be cast off when we die or the rapture happens and we go to heaven. Jesus said furthermore that the new birth is not an option for salvation or to enter the kingdom of God or for eternal life and he used the word "must" in connection with our being born again.
Finally Jesus says we can't predict or foresee the work of the Holy Spirit and who is about to be born of the Holy Spirit as this is a work at God's discretion or free will that we don't completely understand as we also don't understand what place or direction the wind might blow nest. In Greek this word for wind and spirit are the same and carry different aspects of the same original Greek word although other scriptures make clear the Holy Spirit is a Divine Person not just a force. This verse 8 also says the wind representing the Holy Spirit has a will (where it listeth or willeth) to blow or cause people to be born again. We can see the effect of the wind such as blowing leaves or rain or branches or smoke but we can't see the wind itself just as we can see the effects of the Holy Spirit giving a person the born again or spiritual birth new nature but we can't see the Holy Spirit Himself. Lastly it says so is not so was everyone that is born of the Spirit which probably means for true born again Christian the effects of the Holy Spirit should continue to be seen throughout our lives after we are born again not just at the moment we are born again. This is also the scripture passage that God used to persuade me trust Jesus as my personal Lord and Saviour and enter the Kingdom of God. The scripture passage in the Gospel of John 3 that describes the new birth by the Holy Spirit associated with a person trusting in Jesus Christ as their personal Lord and Saviour that he died for our sins and rose from the dead to give us new life is as follows:
There was a Pharesee, named Nicodemus, a ruler of the Jews: 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. Jesus answered and said unto him, Verily, verily(truly), I say unto thee(you), Except a man be born again, he cannot see the kingdom of God. 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? 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. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. Marvel not that I said unto thee, Ye must be born again. The wind bloweth where it listeth (willeth), and thou hearest the sound thereof, but canst not tell whence (from where) it cometh, and whither (to where) it goeth: so is every one that is born of the Spirit. Gospel of John 3:1-8
From natural conception and birth every person, except for Jesus Christ, is ruled by a sinful, selfish nature called in the Bible the flesh. This ungodly nature of the flesh meaning not only preoccupied with the body but also with selfish and sinful thoughts and emotions and spirituality is that it is generally selfish and sinful which leads to continuing spiritual death and if not corrected before physical death to the second death or eternal separation from God and Jesus Christ in hell and then the lake of fire. However the new nature or heart focused on the Holy Spirit leads us to be preoccupied with God and Jesus and His will, word and worship and this is associated with and leads to spiritual and eternal life with God and Jesus and His blessing. The law or the law of Moses attempts to get people to act righteously by external rules and regulations but it doesn't change a person's heart or really get people to obey these commandments of God from the heart. Instead God sent His Son Jesus Christ in the likeness or image of sinful flesh in other words with a very normal except sinless human nature and to address the problem of sin that separates all people from God condemned sin in the flesh by Jesus dying on the cross to pay for all our sins in the flesh with Jesus's substitutionary sinless sacrifice. In this way we can have God's righteousness fulfilled in us who come to be believers in the Lord Jesus Christ by coming to walk not after the law but after the Holy Spirit who comes to reside in us and teach and guide us beginning with the moment we listened to his call to trust in the Lord Jesus Christ for salvation and stop trusting at all in our own merit or righteousness. The scripture reference in Romans 8 of the place of the Holy Spirit in bringing a person to life and fulfillment of the law of God and then walking in it when we take heed to the Holy Spirit's call to our heart to trust in Jesus and His finished work for our righteousness with his death on the cross and resurrection from the dead is as follows:
For the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death. For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh: That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit. Romans 8:2-4
According to this verse in Galatians 3 it is through faith in the Lord Jesus Christ that Christians are partakers of some of the blessings of the Abrahamic Covenant. However these blessings are principly the blessings of salvation through the Messiah in the line of Abraham who is Jesus and do not include the blessing of a promised land to any Gentile country such as the United States as this was a blessing under the Abrahamic covenant only given to God's chosen earthly people the Jews and was not repeated here in Galatians or anywhere else to the church which is God's heavenly people. It is also through the Lord Jesus Christ and our personally placing our faith in Jesus as our personal Lord and Saviour who died for our sins and rose from the dead to give us new life that Christians including many Gentiles or non-Jewish people get the everlasting inheritance of God's indwelling Holy Spirit. The scripture passage from Galatians 3 that mentions that all Christians become partakers of most of the Abrahamic Covenant and get the promise of the indwelling Holy Spirit through faith in the Lord Jesus Christ is as follows:
That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith. Galatians 3:14
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