Concerning Passion and Energy
But in the case of God, it is to be remembered, we speak of wish, but it is not correct to speak of choice. For God does not deliberate, since that is a mark of ignorance, and no one deliberates about what he knows. But if counsel is a mark of ignorance, surely choice must also be so. God, then, since He has absolute knowledge of everything, does not deliberate.
Nor in the case of the soul of the Lord do we speak of counsel or choice, seeing that He had no part in ignorance. For, although He was of a nature that is not cognisant of the future, yet because of His oneness in subsistence with God the Word, He had knowledge of all things, and that not by grace, but, as we have said, because He was one in subsistence. For He Himself was both God and Man, and hence He did not possess the will that acts by opinion or disposition. While He did possess the natural and simple will which is to be observed equally in all the personalities of men, His holy soul had not opinion (or, disposition) that is to say, no inclination opposed to His divine will, nor anything else contrary to His divine will. For opinion (or, disposition) differs as persons differ, except in the case of the holy and simple and uncompound and indivisible Godhead. There, indeed, since the subsistences are in nowise divided or separated, neither is the object of will divided. And there, since there is but one nature, there is also but one natural will. And again, since the subsistences are unseparated, the three subsistences have also one object of will, and one activity. In the case of men, however, seeing that their nature is one, their natural will is also one, but since their subsistences are separated and divided from each other, alike in place and time, and disposition to things, and in many other respects, for this reason their acts of will and their opinions are different. But in the case of our Lord Jesus Christ, since He possesses different natures, His natural wills, that is, His volitional faculties belonging to Him as God and as Man are also different. But since the subsistence is one, and He Who exercises the will is one, the object of the will, that is, the gnomic will, is also one, His human will evidently following His divine will, and willing that which the divine will willed it to will.
Further note, that will (θέλησις) and wish (βούλησις) are two different things: also the object of will (τὸ θελητόν) and the capacity for will (θελητικόν), and the subject that exercises will (ὁ θέλων), are all different. For will is just the simple faculty of willing, whereas wish is will directed to some definite object. Again, the object of will is the matter underlying the will, that is to say, the thing that we will: for instance, when appetite is roused for food. The appetite pure and simple, however, is a rational will. The capacity for will, moreover, means that which possesses the volitional faculty, for example, man. Further, the subject that exercises will is the actual person who makes use of will.
The word τὸ θελήμα, it is well to note, sometimes denotes the will, that is, the volitional faculty, and in this sense we speak of natural will: and sometimes it denotes the object of will, and we speak of will (θέλημα γνωμικόν) depending on inclination.
Source: Exposition of the Faith (New Advent)