Obj. 5: Further, the principal agent in causing the inward effect is that in virtue of which the sacrament operates. But the sacraments derive their power from Christ's Passion and through the invocation of His Name; according to 1 Cor. 1:13: "Was Paul then crucified for you? or were you baptized in the name of Paul?" Therefore Christ, as man, produces the inward sacramental effect.
On the contrary, Augustine (Isidore, Etym. vi) says: "The Divine power in the sacraments works inwardly in producing their salutary effect." Now the Divine power is Christ's as God, not as man. Therefore Christ produces the inward sacramental effect, not as man but as God.
I answer that, Christ produces the inward sacramental effect, both as God and as man, but not in the same way. For, as God, He works in the sacraments by authority: but, as man, His operation conduces to the inward sacramental effects meritoriously and efficiently, but instrumentally. For it has been stated (Q. 48, AA. 1, 6; Q. 49, A. 1) that Christ's Passion which belongs to Him in respect of His human nature, is the cause of justification, both meritoriously and efficiently, not as the principal cause thereof, or by His own authority, but as an instrument, in so far as His humanity is the instrument of His Godhead, as stated above (Q. 13, AA. 2, 3; Q. 19, A. 1).
Nevertheless, since it is an instrument united to the Godhead in unity of Person, it has a certain headship and efficiency in regard to extrinsic instruments, which are the ministers of the Church and the sacraments themselves, as has been explained above (A. 1). Consequently, just as Christ, as God, has power of authority over the sacraments, so, as man, He has the power of ministry in chief, or power of excellence. And this consists in four things. First in this, that the merit and power of His Passion operates in the sacraments, as stated above (Q. 62, A. 5). And because the power of the Passion is communicated to us by faith, according to Rom. 3:25: "Whom God hath proposed to be a propitiation through faith in His blood," which faith we proclaim by calling on the name of Christ: therefore, secondly, Christ's power of excellence over the sacraments consists in this, that they are sanctified by the invocation of His name. And because the sacraments derive their power from their institution, hence, thirdly, the excellence of Christ's power consists in this, that He, Who gave them their power, could institute the sacraments. And since cause does not depend on effect, but rather conversely, it belongs to the excellence of Christ's power, that He could bestow the sacramental effect without conferring the exterior sacrament. Thus it is clear how to solve the objections; for the arguments on either side are true to a certain extent, as explained above. _______________________
FOURTH ARTICLE [III, Q. 64, Art. 4]
Whether Christ Could Communicate to Ministers the Power Which He Had in the Sacraments?
Objection 1: It seems that Christ could not communicate to ministers the power which He had in the sacraments. For as Augustine argues against Maximin, "if He could, but would not, He was jealous of His power." But jealousy was far from Christ Who had the fulness of charity. Since, therefore, Christ did not communicate His power to ministers, it seems that He could not.
Obj. 2: Further, on John 14:12: "Greater than these shall he do," Augustine says (Tract. lxxii): "I affirm this to be altogether greater," namely, for a man from being ungodly to be made righteous, "than to create heaven and earth." But Christ could not communicate to His disciples the power of creating heaven and earth: neither, therefore, could He give them the power of making the ungodly to be righteous. Since, therefore, the justification of the ungodly is effected by the power that Christ has in the sacraments, it seems that He could not communicate that power to ministers.
Obj. 3: Further, it belongs to Christ as Head of the Church that grace should flow from Him to others, according to John 1:16: "Of His fulness we all have received." But this could not be communicated to others; since then the Church would be deformed, having many heads. Therefore it seems that Christ could not communicate His power to ministers.
On the contrary, on John 1:31: "I knew Him not," Augustine says (Tract. v) that "he did not know that our Lord having the authority of baptizing . . . would keep it to Himself." But John would not have been in ignorance of this, if such a power were incommunicable. Therefore Christ could communicate His power to ministers.