You read John 3 in isolation from the fact that St. John the Baptist has already established a form of baptism that created a link between immersion in water and spiritual rebirth, which, of course, echoed the Flood and the passing through the parted sea in Exodus, -- all prefiguring rebirth through baptism. It also ignores Matthew 28:19, where baptism -- the word itself implies water, -- is proclaimed necessary for Christ's plan.
Moreover, your interpretation forces Jesus to mix up a second metaphore of physical birth to the total of three. I thought you were a believer in the perspicuity of the scripture. Consider how, according to you, Nicodemus refers to the physical birth, with great clarity, as birth from the womb in verse 4; Christ in 6 calls is birth of the flesh. But in 5, according to you, Christ abandons the "womb" terminology already offered by Nicodemus in favor of the very unclear "birth of the water", especially unclear in the context of both baptism of John and the scriptural context. In 6, however, Christ already speaks of "flesh". Why did He not stick to the "water" terminology in 6?
Lastly, you agree that the physical birth is "a given", -- we are not in the business of saving souls not yet made, and the unborn babies are not in view of the discussion. So why would Christ state the necessity of physical birth so forcefully, if that is what He is referring to in 5? Nicodemus asked Him about the second birth, not the first.
This is a good example how do-it-yourself scriptural exegesis produces disagreement over a core Christian belief.
"Baptism" does not imply "water", it MEANS "immersion". That could refer to many things, including water. It appears that by your reading of Matthew, that it is man who actually brings down the Holy Spirit on behalf of his fellow man. God does not indwell as He chooses, NO, men make the decision and God is summoned into the baby.
I thought you were a believer in the perspicuity of the scripture.
On the basics, I am, but that doesn't mean that further study isn't needed on finer points. The Bible is a treasure trove that can more than satisfy any appetite.
[On John 3] But in 5, according to you, Christ abandons the "womb" terminology already offered by Nicodemus in favor of the very unclear "birth of the water", especially unclear in the context of both baptism of John and the scriptural context. In 6, however, Christ already speaks of "flesh". Why did He not stick to the "water" terminology in 6?
He didn't abandon the terminology, He confirmed the idea by using a like term, so there would be no confusion. Wasn't it you who said that the Baptisms of John the Baptist didn't have the same effect as they do today? Well, that's all they had at the time, so your argument doesn't "wash". :)
So why would Christ state the necessity of physical birth so forcefully, if that is what He is referring to in 5? Nicodemus asked Him about the second birth, not the first.
He was doing what He always did, explaining something using a point of reference that the hearer could understand. He was saying that all the "newness" you associate with regular birth is similar to the "newness" that goes with rebirth (a new creation).