Except a man be born anew (εαν μη τις γεννηθη ανωθεν). Another condition of the third class, undetermined but with prospect of determination. First aorist passive subjunctive of γενναω. Ανωθεν. Originally "from above" (Mark 15:38), then "from heaven" (John 3:31), then "from the first" (Luke 1:3), and then "again" (παλιν ανωθεν, Galatians 4:9). Which is the meaning here? The puzzle of Nicodemus shows (δευτερον, verse John 3:4) that he took it as "again," a second birth from the womb. The Vulgate translates it by renatus fuerit denuo. But the misapprehension of Nicodemus does not prove the meaning of Jesus. In the other passages in John (John 3:31; John 19:11; John 19:23) the meaning is "from above" (δεσυπερ) and usually so in the Synoptics. It is a second birth, to be sure, regeneration, but a birth from above by the Spirit.
He cannot see the kingdom of God (ου δυνατα ιδειν την βασιλειαν του θεου). To participate in it as in Luke 9:27. For this use of ιδειν (second aorist active infinitive of οραω) see John 8:51; Revelation 18:7.