Merely sufficient grace (gratia mere sufficiens) is that divine assistance whereby God communicates to the human will full power to perform a salutary act (posse) but not the action itself (agere).
The division of grace into efficacious and merely sufficient is not identical with that into prevenient and coöperating. Coöperating grace does not ex vi notionis include with infallible certainty the salutary act. It may indeed be efficacious, but in matter of fact frequently fails to attain its object because the will offers resistance.
a) The existence of efficacious graces is as certain as that there is a Heaven filled with Saints. [pg 042] God would be neither omnipotent nor infinitely wise if all His graces were frustrated by the free-will of man. St. Augustine repeatedly expresses his belief in the existence of efficacious graces. Thus he writes in his treatise on Grace and Free-Will: “It is certain that we act whenever we set to work; but it is He [God] who causes us to act, by giving thoroughly efficacious powers to the will.”[101] And in another treatise: “[Adam] had received the ability (posse) if he would [gratia sufficiens], but he had not the will to exercise that ability [gratia efficax]; for if he had possessed that will, he would have persevered.”[102]
b) Before demonstrating the existence of sufficient grace it is necessary, in view of certain heretical errors, carefully to define the term.
α) Actual grace may be regarded either in its intrinsic energy or power (virtus, potestas agendi) or in its extrinsic efficacy (efficientia, efficacitas). All graces are efficacious considered in their intrinsic energy, because all confer the physical and moral power necessary to perform the salutary act for the sake of which they are bestowed. From this point of view, therefore, and in actu primo, there is no real but a purely logical distinction between efficacious and merely sufficient grace. If we look to the final result, [pg 043] however, we find that this differs according as the will either freely coöperates with grace or refuses its coöperation. If the will coöperates, grace becomes truly efficacious; if the will resists, grace remains “merely sufficient.” In other words, merely sufficient grace confers full power to act, but is rendered ineffective by the resistance of the will.
The inefficacy of merely sufficient grace, therefore, is owing to the resistance of the will and not to any lack of intrinsic power. This is a truth to which all Catholic systems of grace must conform.
Merely sufficient grace may be subdivided into gratia proxime sufficiens and gratia remote sufficiens.
Proximately sufficient grace (also called gratia operationis) confers upon the will full power to act forthwith, while remotely sufficient grace (also termed gratia orationis) confers only the grace of prayer, which in its turn brings down full power to perform other salutary acts.
The gratia orationis plays a most important rôle in the divine economy of grace. God has not obliged Himself to give man immediately all the graces he needs. It is His will, in many instances, as when we are besieged by temptations, that we petition Him for further assistance. “God does not enjoin impossibilities,” says St. Augustine, “but in His injunctions He counsels you both to do what you can for yourself, and to ask His aid in what you cannot do.”[103]
Hence, though grace may sometimes remain ineffective (gratia inefficax = gratia vere et mere sufficiens), it is never insufficient (insufficiens), that is to say, never too weak to accomplish its purpose.