Moreover, when the mind is inclined to a thing, it is no longer impartial between two alternatives. And that to which the mind is more inclined it chooses, unless by a rational discussion, not unattended with trouble, it is withdrawn from taking that side: hence sudden emergencies afford the best sign of the inward bent of the mind. But it is impossible for the mind of man to be so continually watchful as rationally to discuss whatever it ought to do or not to do. Consequently the mind will at times choose that to which it is inclined by the present inclination: so, if the inclination be to sin, it will not stand long clear of sin, thereby putting an obstacle in the way of grace, unless it be brought back to the state of righteousness.
Further we must consider the assaults of passion, the allurements of sense, the endless occasions of evil-doing, the ready incitements of sin, sure to prevail, unless the will be withheld from them by a firm adherence to the last end, which is the work of grace.
Hence appears the folly of the Pelagian view, that a man in sin can go on avoiding further sins without grace. On the contrary the Lord bids us pray: Lead us not into temptation, but deliver us from evil.
But though persons in sin cannot of their own power help putting obstacles in the way of grace, unless they be forestalled by some aid of grace,* still this lack of power is imputable to them for a fault, because it is left behind in them by a fault going before; as a drunken man is not excused from murder, committed in drunkenness, when he gets drunk by fault of his own.* Besides, though this person in sin has it not in his unaided power altogether to avoid sin, still he has power here and now to avoid this or that sin: hence whatever he commits, he voluntarily commits, and the fault is imputed to him not undeservedly.*
3.160 : That it is reasonably reckoned a Man's own Fault if he be not converted to God, although he cannot be converted without Grace
3.162 : That some Men God delivers from Sin, and some He leaves in Sin