Christianity is not about behavior modification or making yourself a better person. We are too far gone to perfect ourselves by patchwork or a few improvements. Rather, the old edifice is so rotten that it must be torn down completely and replaced. Our Lord Jesus Christ did not simply supply one thing that was lacking in us, but everything that was part of our original nature had to be overturned and corrected, since there was nothing but corruption to begin with.
The Bible does not say we were originally something and then God added more to make us better. Instead God shows us that we are less than nothing on our own and that all we have is from above by His gracious hand. When we want to exalt the grace of God as He deserves, we have to confess what we would be on our own and what would become of us if God had not extended His mercy toward us.
John Murray once said, "God effects a change which is radical and all-pervasive, a change which cannot be explained in terms of any combination, permutation, or accumulation of human resources, a change which is nothing less than an new creation by him who calls the things that be not as though they were, who spake and it was done, who commanded and it stood fast. This, in a word, is regeneration."
In other words Murray is explaining that regeneration is not just a mixture or cooperation of the old life and the new life. The new birth is a total, radical, all-pervasive transformation of character. Paul likens it to the creation of the world: "The God who commanded that light shine out of darkness has shined in our heart to give us the light of the knowledge of the glory of God in the face of Jesus Christ."(2 Cor 4:6) perhaps only comparable to the creation of the world in the beginning or new life in birth. Not by any resolve of my own or even a cooperation with God, but by a divine miracle which God alone can accomplish to make me a new creature.