2 Of which the first clause is, “Our Father, which art in heaven.” We have found then a Father in heaven; let us take good heed how we live on earth. For he who has found such a Father, ought so to live that he may be worthy to come to his inheritance. But we say all in common, “Our Father.” How great a condescension! This the emperor says, and this says the beggar: this says the slave, and this his lord. They say all together, “Our Father, which art in heaven.” Therefore do they understand that they are brethren, seeing they have one Father. Now let not the lord disdain to have his slave for a brother, seeing the Lord Christ has vouch-safed to have him for a brother.
3. “Hallowed be Your Name, Your kingdom come.” This hallowing of God's Name is that whereby we are made holy. For His Name is always Holy. We wish also for His kingdom to come; come it will, though we wish it not; but to wish and pray that His kingdom may come, is nothing else than to wish of Him, that He would make us worthy of His kingdom, lest haply, which God forbid, it should come, and not come to us. For to many that will never come, which nevertheless must come. For to them will it come, to whom it shall be said, “Come, you blessed of My Father, receive the kingdom prepared for you from the foundation of the world.” But it will not come to them to whom it shall be said, “Depart from Me, you cursed, into everlasting fire.” Therefore when we say, “Your kingdom come,” we pray that it may come to us. What is, “may come to us”? May find us good. This we pray for then, that He would make us good; for then to us will His kingdom come.
Source: Sermons on Selected Lessons of the New Testament (New Advent)