Because man is a pleasure-driven, pleasure-seeking creature, the knowledge of good and evil was the most treacherous thing to ever be unleashed on mankind. If temptations will always pose themselves as the most immediate satisfaction, and man’s main design is to be satisfied, then man can do nothing but choose evil constantly. Man surrendered their ability to refuse evil when they chose to have the knowledge of good and evil. Evil will always appear as a more imminent satisfaction. Mankind now becomes a slave of a new passion: to carry out evil desires (Galatians 5:16-21). Because mankind rejected God’s law, they became corrupted. As one seed, though as small as a grain of sand, enters into the soil, it sprouts up and overcomes all that stands in its path. This sin laid the seed that would forever give fruit to the weeds of wickedness. All of man’s faculties, their heart, mind, will, soul, became overrun with the vines of sin, corrupting, constricting, and eventually killing man. Sin made all the faculties of man dead to their greatest passion, God.
Apart from the sustaining grace of God, mankind now is totally depraved. Though there is strength left in man and he still bears a marred image of God and can do beneficial things, nothing in the ends of the actions of man is good (Romans 3:10-18). The only thing that can now sustain a man’s choice to do something that is good is the sheer grace of God. I must define good though, lest someone make hash out the understandings of these things. Good is something done in reference to God to glorify him. This is why Paul quotes David’s use of Psalm 14, to show that no man does this in reference apart from some grace of God moving in on a wicked human heart. Apart from the constant sustaining power of God, the human will will always go astray.