John Chrysostom — as excerpted in the Catena Aurea on John 3:9-12

“(Hom. xxvii. 1) Or thus: Be not surprised at His calling Baptism earthly. It is performed upon earth, and is compared with that stupendous birth, which is of the substance of the Father, an earthly birth being one of mere grace. And well hath He said, not, Ye understand not, but, Ye believe not: for when the understanding cannot take in certain truths, we attribute it to natural deficiency or ignorance: but where that is not received which it belongs to faith only to receive, the fault is not deficiency, but unbelief. These truths, however, were revealed that posterity might believe and benefit by them, though the people of that age did not.”