Adam Clarke on John 3:9

How can these things be? - Our Lord had very plainly told him how these things could be, and illustrated the new birth by one of the most proper similes that could be chosen; but so intent was this great man an making every thing submit to the testimony of his senses that he appears unwilling to believe any thing, unless he can comprehend it. This is the case with many - they profess to believe because they comprehend; but they are impostors who speak thus: there is not a man in the universe that can fully comprehend one operation, either of God or his instrument nature; and yet they must believe, and do believe, though they never did nor ever can fully comprehend, or account for, the objects of their faith.