"Jesus answered, “Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. Do not marvel that I said to you, ‘You must be born again.’" John 3:5-7
Christian commentators like to jump forward and look for a means of interpreting this instead of being wise and looking backward. What do you not grasp and understand about "The New Testament is in the Old Testament concealed, and the Old Testament is in the New Testament revealed"? How many times did Jesus and His apostles refer to the "Scriptures"? What is/are "the Scriptures"? The Old Testament!
Without the Old Testament, there is no New Testament. How can I say such a thing? Again, how many times did Jesus and His apostles refer to the "Scriptures"? Again, "The New Testament is in the Old Testament concealed, and the Old Testament is in the New Testament revealed."
Jesus would have been drawing on something from the Old Testament, the "Scriptures." Nicodemus would have understood Him based on his knowledge of the Scriptures. So let us look at two key passages from the Old Testament where the words water and Spirit are brought together in a way that makes sense of this passage.
"For I will pour water on the thirsty land, and streams on the dry ground; I will pour my Spirit upon your offspring, and my blessing on your descendants." Isaiah 44:3
"I will sprinkle clean water on you, and you shall be clean from all your uncleannesses, and from all your idols I will cleanse you. And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh. And I will put my Spirit within you, and cause you to walk in my statutes and be careful to obey my rules." Ezekiel 36:25-27
When Jesus says, "unless one is born again he cannot see the kingdom of God," and, "unless one is born of water and the Spirit, he cannot enter the kingdom of God," He is saying the exact same thing. To a Jewish leader steeped in Old Testament language, the idea of being "born of water and the Spirit" would evoke the idea of the outpouring of the Holy Spirit. Jesus was pointing Nicodemus to the truth of the New Covenant.
Now, according to Baptists, water is associated with "the death, burial, and resurrection of Jesus." [The burial has no actual relevance because Jesus could have hung on the cross for three days and everything would have been accomplished exactly the same. But that is difficult for the religious to grasp.] They derive this conclusion from their wrongly dividing of Romans 6:3-4 in order to support their method of baptism. Romans 6:3-4 has nothing to do with actual water or mode of baptism; it has to do with identification. Pay attention to the context. You can begin with Romans 5:20 and continue from there.
According to Scripture, however, both the Old Testament and the New Testament associate water with the Holy Spirit. Water is not only a symbol of the Holy Spirit, but it is also a symbol for His work. As water cleanses your flesh from dirt, so the Holy Spirit cleanses your inward self of sin. In Acts 10-11, as soon as "the gift of the Holy Spirit was poured out even on the gentiles" (Acts 10:44–45), Peter was immediately reminded of baptism (11:15-16).
Please notice the words used in both Old Testament passages: "pour" and "sprinkle." Right there you have affusion (pouring) and aspersion (sprinkling). As the Spirit was poured out (affusion) on the gentiles, Peter was immediately reminded of baptism. They did not have an abundance of water at hand. In fact, the circumstantial evidence surrounding every single instance of water baptism in the New Testament prevents and prohibits immersion (dunking).
The same is true of John. He would not have invented a new method of baptizing. His baptismal practice would have been derived from the Old Testament Scriptures. In other words, he would have used a hyssop branch to sprinkle (aspersion) water over the people, which he could have done quickly and effortlessly. No doubt, Ezekiel 36:25-27 would have been on John's mind, too, which is why he switched locations from an abundance of water where immersion could take place to "many springs" (John 3:23) where such abundance of water did not exist, but it was cleaner and purer.
I digress. Nevertheless, Jesus' words are not a contrast or comparison between our physical birth and our spiritual birth, and they are not picturing the outward expression of the Christian baptism. He is impressing upon Nicodemus the regeneration of the soul by the Holy Spirit, which was a key promise of the New Covenant. The "born of water and the Spirit" are best understood as a reference to "the washing of regeneration and renewing of the Holy Spirit" (Titus 3:5).