This is probably Augustine's best-known letter. Now known as Letter 130, it was written in the year 412, by which time he had been a bishop for about seventeen years.
Anicia Faltonia Proba was the widow of the wealthiest man in the Roman Empire. Three of her sons held the consulship. After Alaric led a Gothic army into Rome in 410 and pillaged the city, Proba, with a considerable retinue of widows and younger women, took refuge in Africa and established a community of religious women in Carthage. Among her group were her daughter Juliana and her grand-niece Demetrias. (Two years later in 414, Augustine wrote On the good of widowhood to Juliana.) Proba asked Augustine how she ought to pray, and in his response he advised her on the kind of person she ought to be, and what she ought to pray for.
Scholar and author Peter Brown wrote that these ladies, affected by the teachings of Pelagius, elicited Augustine's most mature and sympathetic statements about his ideal for Christian life. Unlike Pelagius, Augustine could find room for a spectrum of human failings. In his own life and in that of others, he sought and encouraged blessedness, in spite of human failings.
This Letter 130 by Augustine to Proba is a short instruction on Christian private prayer. The letter has two parts. Augustine first explains the interior condition desirable for praying (Chapters 1-3). He then (Chapters 4-13) explains the purpose of private prayer is to help the attainment of a blessed life. He suggests that the use of words be kept brief and fervent, and be supported by a life of good works. The words are needed only to help us keep in mind what a person is requesting, and are not necessary to remind or persuade God regarding the request being made. Augustine proclaims that the Lord’s Prayer contains all the praise and petition that prayer requires. A person is free to express the same sentiments in other words if desired, but not to ask for anything that is either contrary to or beyond the scope of the Lord’s Prayer.
In Chapters 10-11 of this second section of Letter 130, Augustine uses the Lord’s Prayer as an example of what he is teaching. He suggested that she should use the Lord's Prayer as a model for all her praying. He advised against the use of an excessive quality of words while praying, and wrote that, instead, good praying involved having the heart pulsing with prolonged fervour directed toward God. He said that most of the time this would consist more in silence than in speaking, and more in tears than in words.
Then Augustine went on to discuss the use of the Lord's Prayer, and admitted the need to use words some of the time. He wrote to Proba: "We, though, need words. They recall to our minds what we are praying for, and allow us to consider it. We shouldn't believe that they inform the Lord or persuade him of anything. When we say, 'Hallowed be your name,' we are admonishing ourselves to desire that his name, which is always holy, may be held to be holy among us humans, that it not be treated with hatred. This is not of advantage to God, but to us."
"When we say, 'Your Kingdom come' - his kingdom will certainly come whether we wish it to or not - we arouse our desire for it, so that it may come to us, and we may be found worthy to reign there. When we say, 'Your will be done, on earth as it is in heaven,' we are asking him for obedience for ourselves, that his will may be done in us as it is done by his angels in heaven."
"When we say, 'Give us this day our daily bread,' by 'this day' we mean this present time. Either we are asking for a sufficiency of what we need, using bread to signify all our needs since bread is first among them; or we are asking for the Sacrament of those who believe, which we require at this present time, to obtain happiness not now but in eternal life. When we say, 'Forgive us our debts, as we forgive our debtors,' we remind ourselves of both what we are to pray for and what we are to do to be worthy to receive it."
"When we say, 'Lead us not into temptation,' we warn ourselves to ask that we not be deprived of God's help, and neither be deceived into consenting to some temptation, nor be so cast down as to yield to it. When we say, 'Deliver us from evil,' we remind ourselves to consider that we are not yet in that good state where we shall suffer no evil."
"This last phrase of the Lord's Prayer is so comprehensive that Christians can use it to express their feelings, they can pour out their tears by using it, in whatever kind of distress they may find themselves. They can start with it, linger over it, and end their prayer with it."
Augustine referred to the Lord's Prayer graphically in a number of his sermons. For example, the Lord's Prayer provides the Christian with a "daily bath" (Sermon 56.12 and also 261.10), and the Lord's Prayer pumps out the bilgewater to prevent it from rising and eventually sinking the ship (Sermon 56.11).
Anicia Faltonia Proba (died in Africa, 432) was a Roman noblewoman. Augustine addressed to her his Letter 130 about the Lord’s Prayer. https://en.wikipedia.org/wiki/Anicia_Faltonia_Proba
Augustine of Hippo: Letter 130 (written in the year 412). From Augustine to Proba. The full text. http://www.newadvent.org/fathers/1102130.htm and http://www.crossroadsinitiative.com/library_article/768/Letter_130_to_Proba_Augustine.html AN2154