Thomas Aquinas

“ Hence it is better to have a thing by merit than without merit. Now since all perfection and greatness must be attributed to Christ, consequently He must have by merit what others have by merit; unless it be of such a nature that its want would detract from Christ's dignity and perfection more than would accrue to Him by merit. Hence He merited neither grace nor knowledge nor the beatitude of His soul, nor the Godhead, because, since merit regards only what is not yet possessed, it would be necessary that Christ should have been without these at some time ”

“ But comprehensors do not merit: because the charity of the comprehensor belongs to the reward of beatitude, since fruition depends upon it. Hence it does not seem to be the principle of merit, since merit and reward are not the same. Therefore Christ before His passion did not merit, even as He does not merit now.
Objection 2: Further, no one merits what is due to him. But because Christ is the Son of God by nature, the eternal inheritance is due to Him, which other men merit by their works. And hence Christ Who, from the beginning, was the Word of God, could not merit anything for Himself. ”

“ Now the human body has divers members of different form, and consequently fitted to divers operations. Therefore in Christ there are divers operations in the human nature.
On the contrary, As Damascene says (De Fide Orth. iii, 15) , "operation is consequent upon the nature." But in Christ there is only one human nature. Therefore in Christ there is only one human operation.
I answer that, Since it is by his reason that man is what he is; that operation is called human simply, which proceeds from the reason through the will, which is the rational appetite. ”

“ Now, as in a mere man the body is moved by the soul, and the sensitive by the rational appetite, so in the Lord Jesus Christ the human nature is moved and ruled by the Divine. Hence they said that there is one indifferent operation on the part of the Godhead operating, but divers things operated, inasmuch as the Godhead of Christ did one thing by Itself, as to uphold all things by the word of His power---and another thing by His human nature, as to walk in body. ”

“ The most loving operation of God is made manifest to us by the supersubstantial Word having taken flesh integrally and truly, and having operated and suffered whatsoever befits His human and Divine operation. ”

“ The sin of an individual harms himself alone; but the sin of Adam, who was appointed by God to be the principle of the whole nature, is transmitted to others by carnal propagation. So, too, the merit of Christ, Who has been appointed by God to be the head of all men in regard to grace, extends to all His members. ”

“ Dionysius places in Christ a theandric, i.e. a God-manlike or Divino-human, operation not by any confusion of the operations or powers of both natures, but inasmuch as His Divine operation employs the human, and His human operation shares in the power of the Divine. Hence, as he says in a certain epistle (Ad Caium iv) , "what is of man He works beyond man; and this is shown by the Virgin conceiving supernaturally and by the unstable waters bearing up the weight of bodily feet." Now it is clear that to be begotten belongs to human nature, and likewise to walk ”

“ And hence it is that Christ's merit extends to others inasmuch as they are His members; even as in a man the action of the head reaches in a manner to all his members, since it perceives not merely for itself alone, but for all the members. ”

“ It would seem that in Christ there are several human operations. For Christ as man communicates with plants by His nutritive soul, with the brutes by His sensitive soul, and with the angels by His intellective soul, even as other men do. Now the operations of a plant as plant and of an animal as animal are different. Therefore Christ as man has several operations.
Objection 2: Further, powers and habits are distinguished by their acts. Now in Christ's soul there were divers powers and habits; therefore also divers operations. ”

“ What things were done and wrought by the one Christ, differ greatly; for some are becoming to God, and some are human, as to walk bodily on the earth is indeed human, but to give hale steps to sickly limbs, wholly unable to walk on the ground, is becoming to God. ”

“ Nevertheless, in a secondary manner anyone may be a cause, to himself, of having certain good things, inasmuch as he cooperates with God in the matter, and thus whoever has anything by his own merit has it, in a manner, of himself. ”