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.
“Psalm 119: "Nun"
In Psalm 119:105, Augustine notes the parallelism. God's Word is a lantern: feet, and a light: paths. He concludes that there is a difference between a light and a lantern. A lantern is created, so it cannot represent Jesus, the uncreated Word of God (Augustine Psalms, loc. 339606, par. 105). For this reason, Augustine considers the use of "light" here to differ from the usage elsewhere in Scripture. The Word, then, is the Scripture.
Verse 106 describes the commitment of the Psalmist, to walk in light of God's judgments (Augustine Psalms, loc. 339618, par. 106). These judgments are worked out, as we do good works motivated by faith. According to verse 107 they also humble us. Augustine considers this to be because of the persecution which is received by those who strive to keep God's commands (Augustine Psalms, loc. 339623, par. 106).
Since we fail to keep God's commands at all times, verse 108 prays that at least the words of the Psalmist's mouth might please God. In the past, Augustine has referred to the sweetness with which God treats his servants. "This passage we explained as the words of one who was gaining in grace, and praying that he might receive in addition to what he had received (Augustine Psalms, loc. 339631, par. 107).
There is some dispute in verse 109, whether it says, "My soul is always in Thy hand" or . . . "my hand." Augustine considers both options, but considers it inconclusive (Augustine Psalms, loc. 339640, par. 108). However, verse 110 suggests "thy hand" is a more appropriate reading. Again, Augustine notes some difficulty with the verb, "I have gained" in verse 111. He considers it to translate best into Latin using two words, which in English indicate, "I have gained in heritage" (Augustine Psalms, loc. 339645, par. 110).
In the end, Augustine observes, we engage in works which are works of righteousness, even if they are temporary, for the good of our neighbor. They are all to be motivated by love.