I answer that, Merit implies a certain equality of justice: hence the Apostle says (Rm. 4:4): "Now to him that worketh, the reward is reckoned according to debt." But when anyone by reason of his unjust will ascribes to himself something beyond his due, it is only just that he be deprived of something else which is his due; thus, "when a man steals a sheep he shall pay back four" (Ex. 22:1). And he is said to deserve it, inasmuch as his unjust will is chastised thereby. So likewise when any man through his just will has stripped himself of what he ought to have, he deserves that something further be granted to him as the reward of his just will. And hence it is written (Lk. 14:11): "He that humbleth himself shall be exalted."
Now in His Passion Christ humbled Himself beneath His dignity in four respects. In the first place as to His Passion and death, to which He was not bound; secondly, as to the place, since His body was laid in a sepulchre and His soul in hell; thirdly, as to the shame and mockeries He endured; fourthly, as to His being delivered up to man's power, as He Himself said to Pilate (Jn. 19:11): "Thou shouldst not have any power against Me, unless it were given thee from above." And, consequently, He merited a four-fold exaltation from His Passion. First of all, as to His glorious Resurrection: hence it is written (Ps. 138:1): "Thou hast known my sitting down"---that is, the lowliness of My Passion---"and My rising up." Secondly, as to His ascension into heaven: hence it is written (Eph. 4:9): "Now that He ascended, what is it, but because He also descended first into the lower parts of the earth? He that descended is the same also that ascended above all the heavens." Thirdly, as to the sitting on the right hand of the Father and the showing forth of His Godhead, according to Is. 52:13: "He shall be exalted and extolled, and shall be exceeding high: as many have been astonished at him, so shall His visage be inglorious among men." Moreover (Phil. 2:8) it is written: "He humbled Himself, becoming obedient unto death, even to the death of the cross: for which cause also God hath exalted Him, and hath given Him a name which is above all names"---that is to say, so that He shall be hailed as God by all; and all shall pay Him homage as God. And this is expressed in what follows: "That in the name of Jesus every knee should bow, of those that are in heaven, on earth, and under the earth." Fourthly, as to His judiciary power: for it is written (Job 36:17): "Thy cause hath been judged as that of the wicked cause and judgment Thou shalt recover."