Reply Obj. 1: Original sin in Adam, which is a sin of the nature, is derived from his actual sin, which is a personal sin, because in him the person corrupted the nature; and by means of this corruption the sin of the first man is transmitted to posterity, inasmuch as the corrupt nature corrupts the person. Now grace is not vouchsafed us by means of human nature, but solely by the personal action of Christ Himself. Hence we must not distinguish a twofold grace in Christ, one corresponding to the nature, the other to the person as in Adam we distinguish the sin of the nature and of the person.
Reply Obj. 2: Different acts, one of which is the reason and the cause of the other, do not diversify a habit. Now the act of the personal grace which is formally to sanctify its subject, is the reason of the justification of others, which pertains to capital grace. Hence it is that the essence of the habit is not diversified by this difference.
Reply Obj. 3: Personal and capital grace are ordained to an act; but the grace of union is not ordained to an act, but to the personal being. Hence the personal and the capital grace agree in the essence of the habit; but the grace of union does not, although the personal grace can be called in a manner the grace of union, inasmuch as it brings about a fitness for the union; and thus the grace of union, the capital, and the personal grace are one in essence, though there is a distinction of reason between them. _______________________
SIXTH ARTICLE [III, Q. 8, Art. 6]
Whether It Is Proper to Christ to Be Head of the Church?
Objection 1: It seems that it is not proper to Christ to be Head of the Church. For it is written (1 Kings 15:17): "When thou wast a little one in thy own eyes, wast thou not made the head of the tribes of Israel?" Now there is but one Church in the New and the Old Testament. Therefore it seems that with equal reason any other man than Christ might be head of the Church.
Obj. 2: Further, Christ is called Head of the Church from His bestowing grace on the Church's members. But it belongs to others also to grant grace to others, according to Eph. 4:29: "Let no evil speech proceed from your mouth; but that which is good to the edification of faith, that it may administer grace to the hearers." Therefore it seems to belong also to others than Christ to be head of the Church.
Obj. 3: Further, Christ by His ruling over the Church is not only called "Head," but also "Shepherd" and "Foundation." Now Christ did not retain for Himself alone the name of Shepherd, according to 1 Pet. 5:4, "And when the prince of pastors shall appear, you shall receive a never-fading crown of glory"; nor the name of Foundation, according to Apoc. 21:14: "And the wall of the city had twelve foundations." Therefore it seems that He did not retain the name of Head for Himself alone.
On the contrary, It is written (Col. 2:19): "The head" of the Church is that "from which the whole body, by joints and bands being supplied with nourishment and compacted groweth unto the increase of God." But this belongs only to Christ. Therefore Christ alone is Head of the Church.
I answer that, The head influences the other members in two ways. First, by a certain intrinsic influence, inasmuch as motive and sensitive force flow from the head to the other members; secondly, by a certain exterior guidance, inasmuch as by sight and the senses, which are rooted in the head, man is guided in his exterior acts. Now the interior influx of grace is from no one save Christ, Whose manhood, through its union with the Godhead, has the power of justifying; but the influence over the members of the Church, as regards their exterior guidance, can belong to others; and in this way others may be called heads of the Church, according to Amos 6:1, "Ye great men, heads of the people"; differently, however, from Christ. First, inasmuch as Christ is the Head of all who pertain to the Church in every place and time and state; but all other men are called heads with reference to certain special places, as bishops of their Churches. Or with reference to a determined time as the Pope is the head of the whole Church, viz. during the time of his Pontificate, and with reference to a determined state, inasmuch as they are in the state of wayfarers. Secondly, because Christ is the Head of the Church by His own power and authority; while others are called heads, as taking Christ's place, according to 2 Cor. 2:10, "For what I have pardoned, if I have pardoned anything, for your sakes I have done it in the person of Christ," and 2 Cor. 5:20, "For Christ therefore we are ambassadors, God, as it were, exhorting by us."