Objection 1. It seems that Christ was not the cause of His own Resurrection. For whoever is raised up by another is not the cause of his own rising. But Christ was raised up by another, according to Acts 2:24: "Whom God hath raised up, having loosed the sorrows of hell": and Romans 8:11: "He that raised up Jesus Christ from the dead, shall quicken also your mortal bodies." Therefore Christ is not the cause of His own Resurrection.
Objection 2. Further, no one is said to merit, or ask from another, that of which he is himself the cause. But Christ by His Passion merited the Resurrection, as Augustine says (Tract. civ in Joan.): "The lowliness of the Passion is the meritorious cause of the glory of the Resurrection." Moreover He asked the Father that He might be raised up again, according to Psalm 40:11: "But thou, O Lord, have mercy on me, and raise me up again." Therefore He was not the cause of His rising again.
Objection 3. Further, as Damascene proves (De Fide Orth. iv), it is not the soul that rises again, but the body, which is stricken by death. But the body could not unite the soul with itself, since the soul is nobler. Therefore what rose in Christ could not be the cause of His Resurrection.
On the contrary, Our Lord says (John 10:18): "No one taketh My soul from Me, but I lay it down, and I take it up again." But to rise is nothing else than to take the soul up again. Consequently, it appears that Christ rose again of His own power.
I answer that, As stated above (50, 2,3) in consequence of death Christ's Godhead was not separated from His soul, nor from His flesh. Consequently, both the soul and the flesh of the dead Christ can be considered in two respects: first, in respect of His Godhead; secondly, in respect of His created nature. Therefore, according to the virtue of the Godhead united to it, the body took back again the soul which it had laid aside, and the soul took back again the body which it had abandoned: and thus Christ rose by His own power. And this is precisely what is written (2 Corinthians 13:4): "For although He was crucified through" our "weakness, yet He liveth by the power of God." But if we consider the body and soul of the dead Christ according to the power of created nature, they could not thus be reunited, but it was necessary for Christ to be raised up by God.
Reply to Objection 1. The Divine power is the same thing as the operation of the Father and the Son; accordingly these two things are mutually consequent, that Christ was raised up by the Divine power of the Father, and by His own power.
Reply to Objection 2. Christ by praying besought and merited His Resurrection, as man and not as God.
Reply to Objection 3. According to its created nature Christ's body is not more powerful than His soul; yet according to its Divine power it is more powerful. Again the soul by reason of the Godhead united to it is more powerful than the body in respect of its created nature. Consequently, it was by the Divine power that the body and soul mutually resumed each other, but not by the power of their created nature.
Source: Summa Theologica (New Advent)