Albert Barnes Commentary John 3:6

"That which is born of the flesh is flesh; and that which is born of the Spirit is spirit." — John 3:6 (ASV)

That which is born of the flesh. To show the necessity of this change, the Savior directs the attention of Nicodemus to the natural condition of man. By that which is born of the flesh, he evidently intends man as he is by nature, in the circumstances of his natural birth. Perhaps, also, he alludes to the question Nicodemus asked, whether a man could be born when he was old? Jesus tells him that if this could be, it would not achieve any valuable purpose; he would still have the same propensities and passions. Another change was therefore indispensable.

Is flesh. Partakes of the nature of the parent. . As the parents are corrupt and sinful, so will be their descendants. . And as the parents are wholly corrupt by nature, so their children will be the same. The word flesh here is used as meaning corrupt, defiled, sinful. The flesh in the Scriptures is often used to denote the sinful propensities and passions of our nature, as these propensities are supposed to have their seat in the animal nature.

"The works of the flesh are manifest, which are these: adultery, fornication, uncleanness, lasciviousness," etc. (Galatians 5:19–20). See also Ephesians 2:3; 1 Peter 3:21; 2:18; 1 John 2:16; Revelation 8:5.

Is born of the Spirit. Of the Spirit of God, or by the agency of the Holy Spirit.

Is spirit. Is spiritual, like the spirit, that is, holy, pure. Here we learn:

1. That all men are by nature sinful.
2. That none are renewed except by the Spirit of God. If man did the work himself, it would still be carnal and impure.
3. That the effect of the new birth is to make men holy.
4. That no man can have evidence that he is born again who is not holy; and just in proportion as he becomes pure in his life will be the evidence that he is born of the Spirit.