Our sinful nature is intertwined with our Imago Dei (image of God).
Envision two plants growing together, which appear as one plant. One of them is a beautiful and fragrant bush, the other a thorn tree. Not only are their trunk and limbs entwined, but their root system is bound upon each other.
Any attempt to destroy the briar would be equally as devastating to the sweet smelling plant. This is the condition in which we find ourselves.
For as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous. Romans 5:19 ESV
When Adam disobeyed in the garden, it was as if his being, physical, spiritual, and moral, had been infected by an insidious virus which changed his identity. Like a science fiction horror movie, this once glorious being became a wreck bent on self destruction, and so changed that he maintained his identity with himself, but no longer recognized his creator.
Sin was not a degenerative condition. It did not take 30 or 100 generations for murder to happen. So we see, that some in their pursuit of religion commit the greatest crimes, while criminals may do acts of heroism. In all walks of life we are confronted by this contradiction.
In this state, man must be saved from the outside. He can’t do anything to count toward his own merit in God’s eyes, for even the good that he does is tainted with the evil of self-justification, pride, selfishness and arrogance. This is what salvation by grace is – a miraculous act of love by a merciful God, who did not leave is in our sin, but came to us in His Son, thereby giving all of himself to save us.
But when the goodness and loving kindness of God our Savior appeared, he saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit, whom he poured out on us richly through Jesus Christ our Savior, so that being justified by his grace we might become heirs according to the hope of eternal life. Titus 3:4-7 ESV