ESV - 5 Jesus answered, "Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
"Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God" (John 3:5): "baptism in water" and receive the "gift of the Holy Spirit". The Kingdom of God is for Spirit Beings (as God, Jesus, and the angels are all Spirit Beings). We (the "Church of God") must become Spirit Beings to enter it; that is, we must be "born again" (resurrection to spirit beings).
The very act of water baptism (John 3:5) is a signature of a covenant: we promise to repent of our sin and God promises to resurrect us from the dead in the last day. Baptism is from the Greek word baptismos meaning "immersion" or submersion in water, which symbolizes our grave, and the coming up or emersion/ emerging from this "watery grave" symbolizes our resurrection from the dead. For the "elects", resurrection means to change from being mortal to immortal Spirit Beings -- thus "born of the Spirit" (because God is Spirit Being).
We are physical beings ("flesh and blood") at our first birth -- spirit beings at our second birth (at our "resurrection from the dead"/ "born again" as symbolized by the "baptism in water and of the Holy Spirit). Note: this is different from "baptism with fire", which is the punishment for sinners.
Jesus always spoke in an order. Whether it was the parable of the tares, the wedding feast, the wise and foolish virgins, or the master who delivered the talents, He always gave two scenarios, which were those who were chosen, and of the kingdom and those who were rejected because they were not the heirs of the King. Some of the virgins were wise, some foolish. But both types meet an end based on their own choices.
Matt 25:3 "Those who were foolish took their lamps and took no oil with them". Matt 25:11,12 "Afterward the other virgins came also, saying, Lord, Lord, open to us!" "But He answered and said, "Assuredly, I say to you, I do not know you."
When speaking with Nicodemus Jesus is doing the same thing. He first states in John 3:3 that unless one is born again, he cannot see the kingdom of God. But then in v.5 He states that unless one is born of water and the Spirit, He cannot enter the kingdom of God.
When someone is born again, he is able to understand that Jesus is the Christ, that Jesus is the only way and that He is the King of the Kingdom. Moses was able to see the promised land but unable to enter it. Heb 3:19 So we see that they could not enter in because of unbelief. Heb 4:1 Therefore, since a promise remains of entering His rest, let us fear lest any of you seem to have come short of it.
This picture is consistent with the parables, like for instance the sower, that one can receive the "seed" (Word of God) even with joy, and yet because it is received in stony places (a hard heart¬ mixed with faith Heb 3:15 & 4:2) but that seed produces no fruit because it has no root. So it's consistent in Christ's teaching that you can hear and believe and yet still not enter, but only "see".
Now going to John 3:5 and the ablity to "enter" the kingdom and not just see the Kingdom of God. It's being born of both water and the spirit which Jesus describes as perquisites to this entry into that Kingdom.
In Isa 44:3-4, The Lord says: for I will pour water on him that is thirsty, and floods upon the dry ground Eph 5:25 husband's love your wives even as Christ also loved the church and gave Himself for it; that He might sanctify it and cleanse it with the washing of water by the Word.
There are many verse which speak of a spiritual water. Rev7:17 For the Lamb which is in the midst of the throne shall feed them and shall lead them unto living fountains of water, and God shall wipe arty all tears from their eyes.
All of these verses (and there are many more) have in common that a spiritual water is at work in the true child of God.
Lastly, Jesus prayed this: John 17:17 Sanctify them by your Truth. YOUR WORD IS TRUTH. There are many who hear the Word, but not everyone is sanctified. Not everyone has the Truth abiding in them, but have only heard the Truth, they aren't being sanctified because while they may have received the Word with joy, they soon returned to their love of the world, riches, flesh, whatever it was that they embraced instead of Christ alone.
To be born of water and The Spirit is to pick up your cross daily and follow Christ, that this world and the ruler of it has no place in you. Jesus said that the way which leads to life is narrow and few find it. In these last days, how much seed is actually finding good soil to grow in and bear fruit? I'm convinced that the majority of "Christians" today are deceived and have only seen, but cannot enter in.