Jesus answered, "Most assuredly I tell you, unless one is born of water and spirit, he can't enter into the Kingdom of God!
Most of the bitterest denunciations against what Jesus taught here are actually directed against a straw man called "baptismal regeneration," in which it is continually affirmed that water cannot save anyone; but, of course, no one supposes that it can.  No efficacy was ever attributed to the water, even by the staunchest defenders of what Jesus here clearly made a precondition of salvation.  Fulminations against baptismal regeneration might have been relevant in Calvin's day, when that scholar attacked the Medieval superstition that a few drops of water sprinkled religiously upon a dead infant could save a soul; but those arguments by Calvin are not relevant arguments against Christ's promise that "He that believeth and is baptized shall be saved" (Mark 16:16).  And that promise is as good a commentary on  John 3:5 as any other (yes, better than any other) that might be brought forward to explain this disputed passage.  The importance of the questions raised around the sacred words of Jesus in this place requires that further attention be directed to their study.  See "Regarding the New Birth" below.