This mode of operation manifestly presupposes a certain weakness of the human will, _i.e._ _concupiscence_, which is an effect of original sin. Actual grace exercises a healing influence on the will(27) and is therefore called _gratia sanans sive medicinalis_. “Unless something is put before the soul to please and attract it,” says St. Augustine, “the will can in no wise be moved; but it is not in man’s power to bring this about.”(28) Concretely, this moral causality of grace manifests itself as a divinely inspired joy in virtue and a hatred of sin, both of which incline the will to the free performance of salutary acts. These sentiments may in some cases be so strong as to deprive the will temporarily of its freedom to resist. The sudden conversion of St. Paul is a case in point. Holy Scripture expressly assures us that God is the absolute master of the human will and, if He so chooses, can bend it under His yoke without using physical force. Cfr. Prov. XXI, 1: “The heart of the king is in the hand of the Lord: whithersoever he will, he shall turn it.” “Who will be so foolish as to say,” queries St. Augustine, “that God cannot change the evil wills of men, whichever, whenever, and wheresoever He chooses, and direct them to what is good?”(29) It is but rarely, of course, that God grants to any man a summary victory over his sinful nature; but this fact does not prevent the Church from praying: “Vouchsafe, O Lord, to compel our wills to thee, even though they be rebellious.”(30) b) Even more important than the moral causality of grace is its physical causality. Man depends entirely on God for the physical strength necessary to perform salutary works. Grace elevates the faculties of the soul to the supernatural sphere, thereby enabling it to perform supernatural acts. Physical is as distinct from moral causality in the order of grace as in the order of nature. The holding out of a beautiful toy will not enable a child to walk without support from its elders. Moral causality is insufficient to enable a man to perform salutary acts. Grace (as we shall show later) is absolutely, _i.e._ metaphysically, necessary for all salutary acts, whether easy or difficult, and hence the incapacity of nature cannot be ascribed solely to weakness and to the moral difficulty resulting from sin, but must be attributed mainly to physical impotence. A bird without wings is not merely impeded but utterly unable to fly; similarly, man without grace is not only handicapped but absolutely incapacitated for the work of salvation. Considered under this aspect, actual grace is called _gratia elevans_, because it elevates man to the supernatural state.(31)