Objection 1. It would seem that judiciary power does not belong to Christ as man. For Augustine says (De Vera Relig. xxxi) that judgment is attributed to the Son inasmuch as He is the law of the first truth. But this is Christ's attribute as God. Consequently, judiciary power does not belong to Christ as man but as God.
Objection 2. Further, it belongs to judiciary power to reward the good, just as to punish the wicked. But eternal beatitude, which is the reward of good works, is bestowed by God alone: thus Augustine says (Tract. xxiii super Joan.) that "the soul is made blessed by participation of God, and not by participation of a holy soul." Therefore it seems that judiciary power does not belong to Christ as man, but as God.
Objection 3. Further, it belongs to Christ's judiciary power to judge secrets of hearts, according to 1 Corinthians 4:5: "Judge not before the time; until the Lord come, who both will bring to light the hidden things of darkness, and will make manifest the counsels of the hearts." But this belongs exclusively to the Divine power, according to Jeremiah 17:9-10: "The heart of man is perverse and unsearchable, who can know it? I am the Lord who search the heart, and prove the reins: who give to every one according to his way." Therefore judiciary power does not belong to Christ as man but as God.
On the contrary, It is said (John 5:27): "He hath given Him power to do judgment, because He is the Son of man."
I answer that, Chrysostom (Hom. xxxix in Joan.) seems to think that judiciary power belongs to Christ not as man, but only as God. Accordingly he thus explains the passage just quoted from John: "'He gave Him power to do judgment, because He is the Son of man: wonder not at this.' For He received judiciary power, not because He is man; but because He is the Son of the ineffable God, therefore is He judge. But since the expressions used were greater than those appertaining to man, He said in explanation: 'Wonder not at this, because He is the Son of man, for He is likewise the Son of God.'" And he proves this by the effect of the Resurrection: wherefore He adds: "Because the hour cometh when the dead in their graves shall hear the voice of the Son of God."
But it must be observed that although the primary authority of judging rests with God, nevertheless the power to judge is committed to men with regard to those subject to their jurisdiction. Hence it is written (Deuteronomy 1:16): "Judge that which is just"; and further on (Deuteronomy 1:17): "Because it is the judgment of God," that is to say, it is by His authority that you judge. Now it was said before (8, 1,4) that Christ even in His human nature is Head of the entire Church, and that God has "put all things under His feet." Consequently, it belongs to Him, even according to His human nature, to exercise judiciary power. on this account. it seems that the authority of Scripture quoted above must be interpreted thus: "He gave Him power to do judgment, because He is the Son of Man"; not on account of the condition of His nature, for thus all men would have this kind of power, as Chrysostom objects (Hom. xxxix in Joan.); but because this belongs to the grace of the Head, which Christ received in His human nature.
Now judiciary power belongs to Christ in this way according to His human nature on three accounts. First, because of His likeness and kinship with men; for, as God works through intermediary causes, as being closer to the effects, so He judges men through the Man Christ, that His judgment may be sweeter to men. Hence (Hebrews 4:15) the Apostle says: "For we have not a high-priest, who cannot have compassion on our infirmities; but one tempted in all things like as we are, without sin. Let us go therefore with confidence to the throne of His grace." Secondly, because at the last judgment, as Augustine says (Tract. xix in Joan.), "there will be a resurrection of dead bodies, which God will raise up through the Son of Man"; just as by "the same Christ He raises souls," inasmuch as "He is the Son of God." Thirdly, because, as Augustine observes (De Verb. Dom., Serm. cxxvii): "It was but right that those who were to be judged should see their judge. But those to be judged were the good and the bad. It follows that the form of a servant should be shown in the judgment to both good and wicked, while the form of God should be kept for the good alone."
Reply to Objection 1. Judgment belongs to truth as its standard, while it belongs to the man imbued with truth, according as he is as it were one with truth, as a kind of law and "living justice" [Aristotle, Ethic. v]. Hence Augustine quotes (De Verb. Dom., Serm. cxxvii) the saying of 1 Corinthians 2:15: "The spiritual man judgeth all things." But beyond all creatures Christ's soul was more closely united with truth, and more full of truth; according to John 1:14: "We saw Him... full of grace and truth." And according to this it belongs principally to the soul of Christ to judge all things.
Reply to Objection 2. It belongs to God alone to bestow beatitude upon souls by a participation with Himself; but it is Christ's prerogative to bring them to such beatitude, inasmuch as He is their Head and the author of their salvation, according to Hebrews 2:10: "Who had brought many children into glory, to perfect the author of their salvation by His Passion."
Reply to Objection 3. To know and judge the secrets of hearts, of itself belongs to God alone; but from the overflow of the Godhead into Christ's soul it belongs to Him also to know and to judge the secrets of hearts, as we stated above (Question 10, Article 2), when dealing with the knowledge of Christ. Hence it is written (Romans 2:16): "In the day when God shall judge the secrets of men by Jesus Christ."
Source: Summa Theologica (New Advent)