8 But what is “in heaven and in earth,” or, “as in heaven so in earth?” The Angels do Your will; may we do it also. “Your will be done as in heaven so in earth.” The mind is heaven, the flesh is earth. When you say (if so be you do say it) with the Apostle, “With my mind I serve the law of God, but with the flesh the law of sin;” the will of God is done in heaven, but not yet in earth. But when the flesh shall be in harmony with the mind, and “death shall be swallowed up in victory,” so that no carnal desires shall remain for the mind to be in conflict with, when strife in the earth shall have passed away, the war of the heart be over, and that be gone by which is spoken, “the flesh lusts against the Spirit, and the Spirit against the flesh; for these are contrary the one to the other; so that you cannot do the things that you would;” when this war, I say, shall be over, and all concupiscence shall have been changed into charity, nothing shall remain in the body to oppose the spirit, nothing to be tamed, nothing to be bridled, nothing to be trodden down; but the whole shall go on through concord unto righteousness, and the will of God will be done in heaven and in earth. “Your will be done in heaven and in earth.” We wish for perfection, when we pray for this. “Your will be done as in heaven so in earth.” In the Church the spiritual are heaven, the carnal are earth. So then, “Your will be done as in heaven so in earth;” that as the spiritual do serve You, so the carnal being reformed may serve You also. “Your will be done as in heaven so in earth.” There is yet another very spiritual meaning of it. For we are admonished to pray for our enemies. The Church is heaven, the enemies of the Church are earth. What then is, “Your will be done as in heaven so in earth”? May our enemies believe, as we also believe in You! May they become friends, and end their enmities! They are earth, therefore are they against us; may they become heaven, and they will be with us.
Source: Sermons on Selected Lessons of the New Testament (New Advent)