Objection 1: It would seem that Christ's Passion did not bring about our salvation efficiently. For the efficient cause of our salvation is the greatness of the Divine power, according to Isa. 59:1: "Behold the hand of the Lord is not shortened that it cannot save." But "Christ was crucified through weakness," as it is written (2 Cor. 13:4). Therefore, Christ's Passion did not bring about our salvation efficiently.
Obj. 2: Further, no corporeal agency acts efficiently except by contact: hence even Christ cleansed the leper by touching him "in order to show that His flesh had saving power," as Chrysostom [*Theophylact, Enarr. in Luc.] says. But Christ's Passion could not touch all mankind. Therefore it could not efficiently bring about the salvation of all men.
Obj. 3: Further, it does not seem to be consistent for the same agent to operate by way of merit and by way of efficiency, since he who merits awaits the result from someone else. But it was by way of merit that Christ's Passion accomplished our salvation. Therefore it was not by way of efficiency.
On the contrary, It is written (1 Cor. 1:18) that "the word of the cross to them that are saved . . . is the power of God." But God's power brings about our salvation efficiently. Therefore Christ's Passion on the cross accomplished our salvation efficiently.
I answer that, There is a twofold efficient agency--namely, the principal and the instrumental. Now the principal efficient cause of man's salvation is God. But since Christ's humanity is the "instrument of the Godhead," as stated above (Q. 43, A. 2), therefore all Christ's actions and sufferings operate instrumentally in virtue of His Godhead for the salvation of men. Consequently, then, Christ's Passion accomplishes man's salvation efficiently.
Reply Obj. 1: Christ's Passion in relation to His flesh is consistent with the infirmity which He took upon Himself, but in relation to the Godhead it draws infinite might from It, according to 1 Cor. 1:25: "The weakness of God is stronger than men"; because Christ's weakness, inasmuch as He is God, has a might exceeding all human power.
Reply Obj. 2: Christ's Passion, although corporeal, has yet a spiritual effect from the Godhead united: and therefore it secures its efficacy by spiritual contact--namely, by faith and the sacraments of faith, as the Apostle says (Rom. 3:25): "Whom God hath proposed to be a propitiation, through faith in His blood."
Reply Obj. 3: Christ's Passion, according as it is compared with His Godhead, operates in an efficient manner: but in so far as it is compared with the will of Christ's soul it acts in a meritorious manner: considered as being within Christ's very flesh, it acts by way of satisfaction, inasmuch as we are liberated by it from the debt of punishment; while inasmuch as we are freed from the servitude of guilt, it acts by way of redemption: but in so far as we are reconciled with God it acts by way of sacrifice, as shall be shown farther on (Q. 49).