To that end he has decreed the salvation of the elect in the way of sin and grace, in order that in and through that salvation He may be glorified. Such is the sovereign and unchangeable will of God. He also wills according to His counsel the accomplishment of that salvation. And He does that not simply in the sense that He wills the redemption of His people through the death of Christ, but in the sense that He wills the complete salvation of the elect in all of its aspects. Therefore regeneration is necessary from God's viewpoint, for it is an integral part of the salvation of His chosen and elect people.
Regeneration is also necessary from the viewpoint of man.
The negative aspect of this necessity is the sin of man. It is the clear teaching of Scripture and the Reformed Confessions that man is totally depraved, conceived and born in sin, incapable of doing any good at all, and inclined to every way of sin and evil. This is true not only from the viewpoint of man's original sin inherited from his first parents, Adam and Eve, but also from the perspective of his own actual sins, those transgressions which every man constantly commits. Moreover, that sin and that sinful nature which man possesses has a center, and that center is his evil heart. The heart in Scripture is pictured as being the center of man's life and existence from a spiritual ethical point of view.