Objection 1. It would seem that the soul of Christ had not omnipotence as regards the execution of His own will. For it is written (Mark 7:24) that "entering into a house, He would that no man should know it, and He could not be hid." Therefore He could not carry out the purpose of His will in all things.
Objection 2. Further, a command is a sign of will, as was said in I, 19, 12. But our Lord commanded certain things to be done, and the contrary came to pass, for it is written (Matthew 9:30-31) that Jesus strictly charged them whose eyes had been opened, saying: "See that no man know this. But they going out spread His fame abroad in all that country." Therefore He could not carry out the purpose of His will in everything.
Objection 3. Further, a man does not ask from another for what he can do himself. But our Lord besought the Father, praying for what He wished to be done, for it is written (Luke 6:12): "He went out into a mountain to pray, and He passed the whole night in the prayer of God." Therefore He could not carry out the purpose of His will in all things.
On the contrary, Augustine says (Qq. Nov. et Vet. Test., qu. 77): "It is impossible for the will of the Saviour not to be fulfilled: nor is it possible for Him to will what He knows ought not to come to pass."
I answer that, Christ's soul willed things in two ways. First, what was to be brought about by Himself; and it must be said that He was capable of whatever He willed thus, since it would not befit His wisdom if He willed to do anything of Himself that was not subject to His will. Secondly, He wished things to be brought about by the Divine power, as the resurrection of His own body and such like miraculous deeds, which He could not effect by His own power, except as the instrument of the Godhead, as was said above (Article 2).
Reply to Objection 1. As Augustine says (Qq. Nov. et Vet. Test., qu. 77): "What came to pass, this Christ must be said to have willed. For it must be remarked that this happened in the country of the Gentiles, to whom it was not yet time to preach. Yet it would have been invidious not to welcome such as came spontaneously for the faith. Hence He did not wish to be heralded by His own, and yet He wished to be sought; and so it came to pass." Or it may be said that this will of Christ was not with regard to what was to be carried out by it, but with regard to what was to be done by others, which did not come under His human will. Hence in the letter of Pope Agatho, which was approved in the Sixth Council [Third Council of Constantinople, Act. iv], we read: "When He, the Creator and Redeemer of all, wished to be hid and could not, must not this be referred only to His human will which He deigned to assume in time?"
Reply to Objection 2. As Gregory says (Moral. xix), by the fact that "Our Lord charged His mighty works to be kept secret, He gave an example to His servants coming after Him that they should wish their miracles to be hidden; and yet, that others may profit by their example, they are made public against their will." And thus this command signified His will to fly from human glory, according to John 8:50, "I seek not My own glory." Yet He wished absolutely, and especially by His Divine will, that the miracle wrought should be published for the good of others.
Reply to Objection 3. Christ prayed both for things that were to be brought about by the Divine power, and for what He Himself was to do by His human will, since the power and operation of Christ's soul depended on God, "Who works in all [Vulgate: 'you', both to will and to accomplish" (Philippians 2:13).
Source: Summa Theologica (New Advent)