Augustine of Hippo

"In the head of the Book it is written of me, that I should fulfil Thy will: O my God, I am willing, and Thy Law is within my heart" [Psalm 40:8]. Behold! He turns His regards to His members. Behold! He hath Himself "fulfilled the will" of the Father. But in what "beginning of a Book" is it written of Him? Perhaps in the beginning of this Book of Psalms. For why should we seek far for it, or examine into other books for it? Behold! It is written in the beginning of this Book of Psalms! …

Exposition on Psalm 40 ↗

Ambrose of Milan

Because there is one will, there is one substance, there is inseparable majesty and the power of the Trinity. But there is another voice, that of the flesh; and yet, it too consents to God's will.… Christ accepted death and crucifixion so as to crucify the flesh. For my sake he took on himself the combat, so that he might conquer me. Though Christ's flesh was strong and not liable to sin, he nevertheless took on my sins. …

Commentaries on the Twelve Davidic Psalms ↗

Thomas Aquinas

Next he shows his resolve to obey, according to his humanity. Now there are two things principally in a person: namely the will and the intellect. The will of a person ought to be subjected to the divine will, and the intellect ought to be directed according to the law of God. And therefore he says, "O my God," Father, insofar as God. Or, "my God," insofar as man, "I have willed to do your will," which is also my will insofar as God; or, "my God," insofar as man, "I have willed to do your will," which is also my will insofar as God. …

Exposition on the Psalms of David ↗