Augustine. Exposition on the Book of Psalms. Schaff, Philip (editor). New York: Christian Literature Publishing Co, 1886. Nicene and Post-Nicene Church Fathers: Series 1: Volume VIII. Re-published 2014, Catholic Way Publishing. Kindle electronic edition, ISBN-13: 978-1-78379-372-3.
Augustine observes that Psalm 91 is the one used by Satan to tempt Jesus in the wilderness. The Christian learns to deal with temptation by seeing how Jesus fought against it (Augustine Psalms, loc. 334730, par. 1). Augustine sees spiritual attacks as different in quality from natural attacks. When oppressed by humans we may well resist and trust that we are suffering like Christ. However, when an attack is of a spiritual nature, we may be more liable to fear (Augustine Psalms, loc. 334737, par. 2). The difference is whether the Christian is trusting in God or not. Verses one and two make it plain that there is no reason for those under God's shadow to fear. Verse three says God delivers his people from snares and from a harsh word. Augustine notes that the devil often uses harsh words to push us into the snare (Augustine Psalms, loc. 334757, par. 4). Even when we face such opposition, we are kept safe under God's wings, like chickens with their mother hen (Augustine Psalms, loc. 334790, par. 5). The metaphor changes from a hen to a soldier in verse five, where we are guarded by truth, a shield.
There is no terror for the one who trusts in God (v. 6). Augustine sees the division of fears at night and at daytime as very important. The terror by day is known to us but that by night is unseen and harms people by surprise (Augustine Psalms, loc. 334810, par. 7). The persecutions at noon, which is hot, could burn us and wither us. Augustine compares this to the shallow soil from the parable of the soils (Augustine Psalms, loc. 334816, par. 8).
In contrast to those who receive persecution, the people who inflict persecutions fall at the right hand of Christ (Augustine Psalms, loc. 334855, par. 10). The evil they wished to do will be done to them.
Verse nine speaks of the Lord as our hope and defense. Augustine sees it as a place to hide not only from temporal persecution but also from wrath and judgment yet to be revealed (Augustine Psalms, loc. 334874, par. 12). He sees it as the holy city, where all the world who believe in Christ can dwell (Augustine Psalms, loc. 334880, par. 13). Verse 11, then, directs our paths so we can come to the holy city. Augustine applies this specifically to Christ. He is our example, whom we must not despise. All the events of His life lead us to the righteousness of God (Augustine Psalms, loc. 334893, par. 14). The temptations of Satan, however, suggest we can do all things without proper dependence on God. Verse 12 continues to speak of God's protection of His people. Yet Augustine points out that the angels who lifted Jesus up to heaven were not superior, but inferior to him. They were returning God the Son to his throne (Augustine Psalms, loc. 334919, par. 16). Again, Augustine sees the Psalm expressing a right dependence on God who has ordered all things rightly, for His glory and our good.
Verse 13 speaks to a victory over various monsters. Augustine is clear that they are symbolic of battles in which the Church has engaged and emerged victorious (Augustine Psalms, loc. 334946, par. 17). God delivers those who depend on Him (vv. 14-15). This message should rescue us from all fear. Augustine lists a number of instances of God's comfort of His people (Augustine Psalms, loc. 334959, par. 19). The goal of all this comfort and care is eternal life (v. 16). Augustine closes his comments by urging his readers to pursue the riches of eternal life.