"Unless one is born of water and the Spirit he cannot enter the kingdom of God"
I used to believe that in the phrase "of water and the Spirit" Jesus was most likely making comparison between the "waters" of natural childbirth and spiritual rebirth. After all, Nicodemus asked the question about entering the mother's womb a second time, right?
However, after further study (and yes, a little introductory education in NT Greek was helpful), I clearly see that this cannot be the case. The phrase is most likely entirely referring to a single entity - baptism in my opinion. It is, by far, the easiest and most natural read of the text. Because they share the same preposition "of", it is HIGHLY IMPROBABLE that it is referring to two separate entities. If Jesus was intending to refer to two entities, the Gospel writer (John) would have either:
1. used two prepositions ("of water and of the Spirit"), or
2. used a comparison sentence structure, such as the statement Jesus makes in verse 6 "That which is born of flesh is flesh; that which is born of spirit is spirit."
Of course, I am not a Greek scholar, I do not pretend to be one, and I doubt that even with seminary training, I will ever be one. Theologians will undoubtedly continue to vigorously debate the meaning of this passage. However, it appears to be simple enough to me. Jesus is talking about baptism. Period.
Also, suggesting that Jesus might be referring to natural childbirth poses an additional problem:
If God's Word is 100% true... 100% accurate, then this passage would be suggesting that "being born [through waters of childbirth]" was a requirement for entering the kingdom of heaven. That, in turn, would suggest that all children who die from abortion, stillbirth, or miscarriage are eternally doomed. God's Word is silent on the eternal destiny of such souls, and as a Bible believing Lutheran, I believe that we too must be very careful about any attempt to speak truth where the Bible is silent. It's okay to form opinions about such things as long as we aren't being presumptious to know the mind of God or speak where the Word is silent.
On the other hand, if being born naturally is not a requirement for salvation, why would our Lord even mention it? "Well... first of all you need to be born..." That would be the classic "DUHHHH!" statement of all eternity. Nicodemus understands natural childbirth... the question seems to be rhetorical in nature; Jesus is essentially saying, "no, I'm talking about things of the Spirit... you've been formally trained in the teachings of God, and you don't seem to understand the things of the Spirit."
As a Lutheran, it's quite tempting to launch into a discussion about the question of baptismal regeneration, but I'll skip that...at least for now. :-)