John 3:7

7. Marvel not When, in John 3:4, Nicodemus in surprise demands how a man could be born again, Jesus in John 3:5 reiterates the statement, and in John 3:6 explains it: but so explains it as to leave it in its own true mystery. It is by nature indeed a second birth; not of body, but something in itself quite as wonderful and far more radical; namely, a second birth of spirit, and by the Spirit. Nicodemus pauses in an utter marvel! Jesus then finally and calmly utters this Marvel not; and then proceeds to reaffirm the doctrine, with an illustration intended to soothe his perturbation.

Ye must Must, and not ye, is the emphatic word. The protest of Nicodemus is not (as Alford imagines) against his own being born again; whether as an old man, or as a doctor, or as a duly circumcised Jew. It is against a renovation of the soul by the Holy Spirit in ANY case. This is clear from the fact that the illustration which now follows touches not merely the regeneration of a Jew, but of a human being.