5 There follows next, “Give us this day our daily bread.” It may be understood simply that we pour forth this prayer for daily sustenance, that we may have abundance: or if not that, that we may have no want. Now he said “daily,” for as long as it is called “today.” Daily we live, and daily rise, and are daily fed, and daily hunger. May He then give us daily bread. Why did He not say “covering” too, for the support of our life is in meat and drink, our covering in raiment and lodging. Man should desire nothing more than these. Forasmuch as the Apostle says, “We brought nothing into this world, neither can we carry anything out: having food and covering, let us be therewith content.” Perish covetousness, and nature is rich. Therefore if this prayer have reference to our daily sustenance, since this is a good understanding of the words, “Give us this day our daily bread;” let us not marvel, if under the name of bread other necessary things are also understood. As when Joseph invited his brethren, “These men,” says he, “will eat bread with me today.” Why, were they to eat bread only? No, but in the mention of bread only, all the rest was understood. So when we pray for daily bread, we ask for whatever is necessary for us in earth for our bodies' sake. But what says the Lord Jesus? “Seek ye first the kingdom of God and His righteousness, and all these things shall be added unto you.” Again, this is a very good sense of, “Give us this day our daily bread,” your Eucharist, our daily food. For the faithful know what they receive, and good for them it is to receive that daily bread which is necessary for this time present. They pray then for themselves, that they may become good, that they may persevere in goodness, and faith, and a holy life. This do they wish, this they pray for; for if they persevere not in this good life, they will be separated from that Bread. Therefore, “Give us this day our daily bread.” What is this? Let us live so,that we be not separated from Your altar. Again, the Word of God which is laid open to us, and in a manner broken day by day, is “daily bread.” And as our bodies hunger after that other, so do our souls after this bread. And so we both ask for this bread simply, and whatsoever is in this life needful both for our souls and bodies, is included in “daily bread.”
6. “Forgive us our debts,” we say, and we may well say so; for we say the truth. For who is he that lives here in the flesh, and has no debts? What man is there that lives so, that this prayer is not necessary for him? He may puff himself up, justify himself he cannot. It were well for him to imitate the Publican, and not swell as the Pharisee, “who went up into the temple,” and boasted of his deserts, and covered up his wounds. Whereas he who said, “Lord, be merciful to me a sinner,” knew wherefore he went up. This prayer the Lord Jesus, consider, my brethren, this prayer the Lord Jesus taught His disciples to offer, those great first Apostles of His, the leaders of our flock. If the leaders of the flock then pray for the remission of their sins, what ought the lambs to do, of whom it is said, “Bring young rams unto the Lord”? You knew then that you have repeated this in the Creed, because among the rest you have mentioned there “the remission of sins.” There is one remission of sins which is given once for all; another which is given day by day. There is one remission of sins which is given once for all in Holy Baptism; another which is given as long as we live here in the Lord's Prayer. Wherefore we say, “Forgive us our debts.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)