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 109, in its speaking of the betrayer, makes a prophecy about Christ. Augustine takes the reference to Judas to also speak of Christ, due to their interaction (Augustine Psalms, loc. 338078, par. 1).
The Psalm first calls for God to protect the godly, due to those who speak in ungodly ways (Augustine Psalms, loc. 338083, par. 2). The ungodly speak with a variety of lies, as reflected in verse two. Augustine points out that Jesus' opponents both called him "Good Master" and called for his death (Augustine Psalms, loc. 338088, par. 3). Verse three speaks of the opponents' work. Augustine discusses these works in six different classes, commenting very briefly on how they are various ways of pursuing the same end, harm to Jesus, the one who is good (Augustine Psalms, loc. 338098, par. 4). Augustine concludes that Christians should do what Jesus did, by repaying evil with Good and by praying for those who would oppose us (Augustine Psalms, loc. 338109, par. 5). Verse four describes the evildoers as paying hatred in exchange for good. This leads the Psalmist to speak of what the opponents receive due to their hostility (Augustine Psalms, loc. 338115, par. 7).
Verse five returns us to an individual, an ungodly ruler. Augustine again identifies this as Judas, who betrayed Christ (Augustine Psalms, loc. 338125, par. 8). According to verse six even the prayers of the unrighteous one are sin. augustine continues to relate this to Judas, who did not pray to Christ (Augustine Psalms, loc. 338130, par. 9). His days became few (v. 7), in the case of Judas, due to his death. The interpretation of Peter in Acts was that this required selection of a replacement apostle (Augustine Psalms, loc. 338140, par. 11(.
The death of Judas, and perhaps of all the opponents of Christ, results in harm to family members as well (Augustine Psalms, loc. 338140, par. 11). This state of harm may be permanent. By verse 12 the posterity are gone. Augustine takes this to be related to God's threat that the sins of the fathers would affect the children (Augustine Psalms, loc. 338151, par. 14). Verse 14 emphasizes that the evil would always be opposed to God. Their failure to act in mercy results in the loss of even the memory of their family. Verses 15-16 describe the possible outcome of the work of the wicked (Augustine Psalms, loc. 338161, par. 16). The persecution may eventually be poured out on the poor. Augustine takes verse 17 to apply beyond the case of Judas. The evildoer delights in cursing, such as the Pharisees did when they asked that Jesus' blood (guilt) would be on them and their children (Augustine Psalms, loc. 338171, par. 17). Verse 18 goes on to describe the boasting and evil words as a garment. Augustine finds this language to speak of the wicked man's own works, not anything given to him or imposed upon him (Augustine Psalms, loc. 338187, par. 19).
In verse 20 the Psalmist calls on the Lord, asking for mercy (Augustine Psalms, loc. 338192, par. 20). Verses 21-22 speak to the frailty of the Psalmist. Our humanity seems poor and weak. Again, Augustine can apply all the descriptions to Christ, as he endured all the trials common to humans (Augustine Psalms, loc. 338212, par. 23).
In the final analysis, in verse 26, all that happens is from the hand of the Lord (Augustine Psalms, loc. 338227, par. 26). God rises above all the evil, blessing the evil in verse 27. The same slanderers who are blessed in verse 27 should be ashamed of their works and attitude (Augustine Psalms, loc. 28). True praise belongs to God, not to man. He is the one who cares for the poor (v. 30) (Augustine Psalms, loc. 338243, par. 30).