Ecc 12:7 Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it.
Surely Solomon knew about the existence of man's flesh and his spirit...That however is not the conversation Jesus is having with Nicodemus...
While Nicodemus clearly understands the makeup of the human, Nick was completely clueless about the the Spirit of God indwelling the believer in the New birth...
Nicodemus was acutely aware of his first birth but was shocked to hear and learn that he must also be born from above without the aid of his mother...Nicodemus had to become born 'again'...The first time from his mother in the flesh, and the second time with the indwelling of the Holy spirit which was not given to Nicodemus or anyone at their first, natural birth...
Obviously Solomon understood there are two different separate bodies, but Nicodemus did not know or understand. We can know this by what Christ asked him in verse 10, the instructed him (Nicodemus) in verses 11 and 12. The complete point up to now for us all is given in verse 13.
Surely Solomon knew about the existence of man's flesh and his spirit...That however is not the conversation Jesus is having with Nicodemus... While Nicodemus clearly understands the makeup of the human, Nick was completely clueless about the the Spirit of God indwelling the believer in the New birth... Nicodemus was acutely aware of his first birth but was shocked to hear and learn that he must also be born from above without the aid of his mother...Nicodemus had to become born 'again'...The first time from his mother in the flesh, and the second time with the indwelling of the Holy spirit which was not given to Nicodemus or anyone at their first, natural birth...
Nicodemus was a Pharisee, but knew by what he secretly said to Christ, there was something different about Christ. We know that by what Nicodemus says to Christ in secret.
Christ did not speak about the Holy Spirit to Nicodemus as that bit of instruction did not come until much later, also described as The Comforter that would be after Christ return back to Heaven.
What Christ was telling Nicodemus was what was required of any and all to 'see' the kingdom of God. Christ did not say anything about anyone receiving the Holy Spirit as that was not the subject. What Christ said was required to 'see' the kingdom of God was to be born of woman. AND as we find in other places some sons of God refused to be born of woman, and instead left their estate and came directly here and set up housekeeping with the daughters of Adam.
It might help if a search was done on the 'Greek' word translated 'again' in John 3:3, to learn the other places the original Greek word was used and how it was translated. As John 3 is not about the Holy Spirit or The Comforter which was sent after the Ascension of Christ.