We have said that God is the primary cause of our good acts. When man rejects grace and chooses something sinful, God the Creator preserves him in being, and even moves him according to his own choice . . . enabling the sinner to carry out the sinful action. But God in no way is the cause of the sinful choice which is the sin. In fact, God gave him sufficient grace to choose otherwise. In every sin that man commits he rejects an actual grace offered by God to draw him to, and enable him to choose, the good.
Sin is the one and only thing of which sinful man is the total cause .
After repeated rejections of God s grace, the sinner s heart can become hardened, and his mind blinded to the lights and inspirations received. Then only a special gift of God s mercy will penetrate that blind resistance. But with God all things are possible. To preserve the gift of grace received at baptism lest it be lost through grave sin. It is also common teaching that one who loses the state of grace through grave sin, and deliberately remains in that state, cannot remain long without committing additional grave sins, for as St. Gregory the Great says, a sin not at once taken away by repentance, by its weight drags us down to other sins.