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 (Question [48], Articles [1],6; Question [49], Article [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 (Question [13], Articles [2],3; Question [19], Article [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 (Article [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 (Question [62], Article [5]). And because the power of the Passion is communicated to us by faith, according to Rm. 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.