John 3:9

“Nicodemus answered and said unto him, etc.] Remaining still as ignorant as ever, though Christ had explained the phrase “born again”, at which he stumbled, by a being “born of water and of the Spirit”, or of the grace of the Spirit of God; and had illustrated this by the free, powerful, and invisible blowing of the wind: how can these things be? The Arabic version reads, “how can this be?” referring either to the last thing said, that a man’s being born of the Spirit, is like the blowing of the wind; or to the explanation of the first expression, that a man should be born of water, and of the Spirit; or to the first assertion itself, that a man should be born again; which notwithstanding the…”

“How, &c.--Though the subject still confounds Nicodemus, the necessity and possibility of the new birth is no longer the point with him, but the nature of it and how it is brought about [LUTHARDT]. "From this moment Nicodemus says nothing more, but has sunk unto a disciple who has found his true teacher. Therefore the Saviour now graciously advances in His communications of truth, and once more solemnly brings to the mind of this teacher in Israel, now become a learner, his own not guiltless ignorance, that He may then proceed to utter, out of the fulness of His divine knowledge, such farther testimonies both of earthly and heavenly things as his docile scholar may to his own profit receive"…”

“How can these things be? - Nicodemus was still unwilling to admit the doctrine unless he understood it; and we have here an instance of a man of rank stumbling at one of the plainest doctrines of religion, and unwilling to admit a truth because he could not understand “how” it could be, when he daily admitted the truth of facts in other things which he could as little comprehend. And we may learn: 1.That people will often admit facts on other subjects, and be greatly perplexed by similar facts in religion. 2.That no small part of people’s difficulties are because they cannot understand how or why a thing is. 3.That people of rank and learning are as likely to be perplexed by these things as…”

“How: Joh 3:4, Joh 6:52, Joh 6:60; Pro 4:18; Isa 42:16; Mar 8:24, Mar 8:25; Luk 1:34 John 3:10”