The reason Jesus mentioned being born of water and also being born of the spirit is because he first said a man must be born again, very simple, then Nicodemus asked how can a man be born when he is old, can he ENTER INTO HIS MOTHERS WOMB AND BE BORN. Jesus answered this question and added to the original statement "you must be born again". Jesus added that which is born of the flesh is flesh( this would be a person coming out of h the mothers womb when the water breaks, born of water. But the spirit al birth is unseen born of the spirit, like the wind. If water baptism was mean with the spirit here then when a person gets water baptized you would see it. But jesus said the new birth is unseen like the wind. so is everyone that is born of the spirit. He did not end the talk with "born of the spirit and water.
also Nicodemus may have thought he was saved just by his natural birth being a child in Israel from Abraham etc. But Jesus corrects any misunderstanding of this.
notice the order and flow of this section
"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. [Jesus first simply mentions being born again]
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? [Nicodemus then ask how a man can go into his mothers womb and be born, so the context does refer in part to a natural birth, or being born after the flesh, for flesh is flesh as jesus said, and the baby comes out of the womb with water , when the water breaks, to e born of water is an expression of this, very simple really to the unbiased reader]
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. [ Jesus answers Nicodemus question and shows a difference in the two births, Jesus is saying that none enter into the kingdom of God unless they have two births, not just one as Nicodemus had, just by claiming to be a descendant of Abraham and belonging to the Jews did not make them saved as many may have thought, something else is needed and that is to be born of the spirit.]
6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. [This is so clear her that I marvel any could miss it. Two births are mentioned in this section, one is of the flesh and that birth is only flesh, NOT a spiritual birth in any way), the other is to be born after the spirit and this is by the word of God as scripture teaches]
7 Marvel not that I said unto thee, Ye must be born again. [ Jesus now goes away from answering Nicodemus question about being born a second time from the womb of a woman and clarifies his original words in vs 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. [Here we see that the expression to be born again is a spiritual one not of the flesh but of the spirit, like the wind which cannot be seen so is everyone that is born of the spirit. Notice here Jesus does not mention born of the flesh or born of water. He simply reaffirms his original words in vs 3 about being g born again. This birth is from above not of the earth. this birth is a spiritual birth[
Paul says similar about this birth here,
Galatians 4:19
My little children, of whom I
travail in birth again until
Christ be formed in you,..."
Notice here that the birth he speaks of is a spiritual one. They had already received the spirit by the hearing of faith in Chapter three we read , and then they were trying to be perfect by the works of the law and adding the law and circumcision to the gospel. This caused some to fall from grace ( or salvation for by grace are ye saved) and they had to be born again, again, as Paul said. But there is no water baptism mentioned here. To have "birth again", is to have Christ formed in you. This is a spiritual life. If any try to add water baptism to the gospel , they fall into the game judgement Paul warned about adding circumcision to salvation also. The gospel is 1 Cor 15: 1-4, plain and simple, no works of the law added no water baptism or Sabbaths or circumcision etc.
To be born again is a spiritual life not physical, not water or ritual . We see this here
"23 Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever."
It is the word of God that gives life and birth and this word is sown in the heart,
"9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God." ( 1 John 3:9)
an
"18 Of his own will begat he us with the word of truth,...and receive with meekness the engrafted word, which is able to save your souls."( James 1:18,21)
Psalm 119:50
"This is my comfort in my affliction: for
thy word hathquickened me."
Nicodemus should have known this already as jesus said. Quickened means to make alive.
Ephesians 2:1
And you hath he
quickened, who were dead in trespasses and sins;"
Ephesians 2:5
Even when we were dead in sins, hath
quickened us together with Christ, (by grace ye are saved)
this last verse is important because by grace we are saved not of works. Not of water baptism. Paul said Christ sent him not to baptism but to preach the gospel. This shows the difference of water baptism to the gospel, and they are not the same. Yet the gospel is what saves as Paul said in 1 Cor 15.