Alcuin
Catena Aurea · Johannesevangelium 3
Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother’s womb, and be born? Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. Marvel not that I said unto thee, Ye must be born again. The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth; so is every one that is born of the Spirit.
Therefore, Thou knowest not whence it cometh, or whither it goeth; for, although the Spirit should possess a person in thy presence at a particular time, it could not be seen how He entered into him, or how He went away again, because He is invisible.