Father Pegues notes that the human body of Christ possessed great perfection and beauty because “such belonged to the dignity of the Word of God, who was hypostatically united to this Body; and such was due also to the action of the Holy Ghost, by whom this Body was formed directly in the womb of our Blessed Lady.”
Nevertheless, Christ took on certain defects in His human body and human soul because “such were necessary for the end of the Incarnation, which was to make satisfaction for our sins—to come on earth as one of us—to be for us an example by the practice of the highest virtues.”
He took upon Himself these defects in His human body: “all those defects or miseries and infirmities which are to be found in the whole of human nature as a result of Adam’s sin, such as hunger, thirst, death, and so on; but in Christ there were none of those defects that are the result of personal sin or of heredity.”
He took upon Himself these defects in His human soul: “the capability of feeling pain, especially the sufferings inflicted upon His Body during the course of His Passion; all the interior affective motions, whether of the sensitive or intellectual order; in other words, Christ had the passions such as sadness, fear, anger, etc., except that all these passions were in perfect accord with His reason, to which they were always perfectly subjected.”
We say in all truth that God is man and that Jesus Christ is God, for we are speaking of the one same divine person Who possesses two complete natures, namely, the divine nature and a human nature. “He is one being only, God and man together; and this by reason of the unity of Person which subsists in both the human and the divine natures.” Since Christ has two natures, He has two wills: “In Him there is the divine will in so far as He is God; and the human will in so far as He is man.” His human will, like every human will, is a free will, although “it was absolutely impossible for Him to sin, His will being always and in every sense conformed to the divine will.”
Quotations from Thomas Pegues, Catechism of the “Summa Theologica” of Saint Thomas Aquinas, trans. Aelred Whitacre (New York: Benziger, 1922).