The Enchiridion by St. Augustine
Chapter 116.--Luke Expresses the Substance of These Seven Petitions More Briefly in Five.
But the Evangelist Luke in his version of the Lord's prayer embraces not seven, but five petitions: not, of course, that there is any discrepancy between the two evangelists, but that Luke indicates by his very brevity the mode in which the seven petitions of Matthew are to be understood. For God's name is hallowed in the spirit; and God's kingdom shall come in the resurrection of the body. Luke, therefore, intending to show that the third petition is a sort of repetition of the first two, has chosen to indicate that by omitting the third altogether. Then he adds three others: one for daily bread, another for pardon of sin, another for immunity from temptation. And what Matthew puts as the last petition, |but deliver us from evil,| Luke has omitted, to show us that it is embraced in the previous petition about temptation. Matthew, indeed, himself says, |but deliver,| not |and deliver,| as if to show that the petitions are virtually one: do not this, but this; so that every man is to understand that he is delivered from evil in the very fact of his not being led into temptation.