King David declared, “Behold, I was shapen in iniquity; and in sin did my mother conceive me” (Ps. 51:5). He described his depravity as innate and not created, as derived from his mother and not his Maker, showing that defilement is transmitted directly from Adam. The same fact was expressed by Jesus Christ when He said, “That which is born of the flesh is flesh” (John 3:6). In the Old Testament the word “flesh” is used as a general term for human nature or mankind: “Let all flesh bless his holy name” (Ps. 145:21) —that is, all men; “All flesh is grass” (Isa. 40:6)—the life of every member of our race is frail and fickle.
The term occurs in the New Testament in the same sense: “Except those days should be shortened, there should no flesh be saved” (Matt. 24:22); “By the deeds of the law there shall no flesh be justified in his sight” (Rom. 3:20)—by his own obedience no man can merit acceptance with God.
But since mankind is fallen and human nature is depraved, the term “flesh” becomes the expression of that fact; and every time it is used in Scripture in a moral sense it refers to the corruption of our entire beings, without any distinction between our visible and invisible parts—body and mind. This is evident from those passages where “the flesh” is contrasted with “the spirit” or the new nature (Rom. 8:5-6; I Cor. 2:11; Gal. 5:17). When the apostle declared, “For I know that in me (that is, in my flesh), dwelleth no good thing” (Rom. 7:18), he had reference to far more than his body with its appetites, namely, his entire natural man, with all its faculties, powers and propensities. The whole was polluted, and therefore nothing good could issue from him until divine grace was imparted.
Thus it is clear that when Christ declared, “That which is born of the flesh is flesh” He signified that that which is propagated by fallen man is depraved, that whatever comes into this world by ordinary generation is carnal and corrupt, causing the heart itself to be deceitful above all things and desperately wicked. It is evident also from the immediate context (John 3:3-5), for what He affirmed in verse 6 was in order to demonstrate the absolute need of regeneration. Jesus Christ was contrasting the first birth with the new birth, and showing how imperative is the latter because we are radically tainted from the outset. All of us by nature are essentially evil, nothing but “flesh”; everything in us is contrary to holiness.
The faculties which men receive at birth have a carnal bias, an earthly trend, a distaste for the heavenly and divine, and are inclined only to selfish aims and groveling pursuits. In the most polished or religious society, equally with the vulgar and profane, “that which is born of the flesh is flesh” and can never be anything better.
Prune and trim a corrupt tree as much as you will, it can never be made to yield good fruit. Every man must be born again before he can be acceptable to a holy God.