7 “Your will be done.” What! If you say not this, will not God do His will? Remember what you have repeated in the Creed, “I believe in God the Father Almighty.” If He be Almighty, why do you pray that His will may be done? What is this then, “Your will be done”? May it be done in me, that I may not resist Your will. Therefore here again it is for yourself you pray, and not for God. For the will of God will be done in you, though it be not done by you. For both in them to whom He shall say, “Come, you blessed of My Father, receive the kingdom prepared for you from the beginning of the world;” shall the will of God be done, that the saints and righteous may receive the kingdom; and in them to whom He shall say, “Depart ye into everlasting fire, prepared for the devil and his angels,” shall the will of God be done, that the wicked may be condemned to everlasting fire.
That His will may be done by you is another thing. It is not then without a cause, but that it may be well with you, that you dost pray that His will may be done in you. But whether it be well or ill with you, it will still be done in you: but O that it may be done by you also. Why do I say then, “Your will be done in heaven and in earth,” and do not say, “Your will be done by heaven and earth?” Because what is done by you, He Himself does in you. Never is anything done by you which He Himself does not in you. Sometimes, indeed, He does in you what is not done by you; but never is anything done by you, if He do it not in you.
Source: Sermons on Selected Lessons of the New Testament (New Advent)