Human nature in its fourfold state ... In several practical discourses

Thirdly, Consider the confession of the Psalmist David, Psal. li. 6. Behold I was shapen in iniquity, and in sin did my mother conceive me. Here he ascends from his actual sin, to the fountain of it, namely, corrupt nature. He was a man according to God's own heart; but from the beginning it was not so with him. He was begotten in lawful marriage; but when the lump was shapen in the womb, it was a sinful lump. Hence the corruption of nature is called the old man; being as old as ourselves, older than grace, even in those that are sanctified from the womb.

Fourthly, Hear our Lord's determination of the point, John iii. 5. That which is born of the flesh, is flesh. Behold the universal corruption of mankind, all are flesh. Not that all are frail, tho' that is a sad truth too; yea, and our natural frailty is an evidence of our natural corruption; but that is not the sense of this text: but here is the meaning of it, all are corrupt and sinful, and that naturally: hence our Lord argues here, that because they are flesh, therefore they must be born again, or else they cannot enter into the kingdom of God, ver. 3, 5. And as the corruption of our nature evidenceth the absolute necessity of regeneration; so the absolute necessity of regeneration plainly proves the corruption of our nature: for why should a man need a second birth, if his nature were not quite marred in the first birth? Infants must be born again, for that is an except (John iii. 3) which admits of no conception. And therefore, they were circumcised under the Old Testament, as having the body of the sins of the flesh, (which is conveyed to them by natural generation) to put off, Col. ii. 11. And now by the appointment of Jesus Christ, they are to be baptized; which says they are unclean, and that there ⟨p. 37⟩is no salvation for them, but by the washing of regeneration, and renewing of the Holy Ghost,