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 prefaces his comments on Psalm 99 with a reminder that the Christian considers all the Old Testament to look forward to Christ (Augustine Psalms, loc. 336101, par. 1). Verse one says there is anger in response to the Lord's status as king. Augustine observes that those who are angry are responding to the fact that the real God is reigning, rather than the gods of their own creation (Augustine Psalms, loc. 336106, par. 2). The anger of God's opponents does not accomplish their purpose. Their idols still perish and God is still the king. He sits on his heavenly throne (Augustine Psalms, loc. 336121, par. 3). Verse two speaks of the Lord's tgreatness, "in Sion, and high above all people." Augustine recalls that Zion implies watchfulness (Augustine Psalms, loc. 336140, par. 4). This, then, is the Church, a city which looks to God.
Augustine notes that the opponents of God are angry with the Church, but that Christians should not be angry with their opponents. Rather, they pray for their persecutors (Augustine Psalms, loc. 336146, par. 5). The Church, then, confesses God's great name (v. 3). Augustine observes that God's name is known in all the nations, and is proclaimed by His people (Augustine Psalms, loc. 336161, par. 6). As he frequently does, Augustine bases our knowledge of God's greatness on our confidence that He is the just judge. In the same way, Christians are to engage in just judgment (Augustine Psalms, loc. 336171, par. 7).
Verse five calls us to magnify the Lord. His people worship before him due to his greatness (Augustine Psalms, loc. 336176, par. 8). Augustine observes that the earth is seen as God's footstool in Scripture. The desire to worship at his footstool is easily confused with worship of the earth (Augustine Psalms, loc. 336181, par. 8). The material, earthly things are important. Yet we look to Christ, the one with real flesh and blood, for our hope (Augustine Psalms, loc. 336191, par. 8).
In verse six the Psalm turns to a history of God's people, those who hear from him and call upon him (Augustine Psalms, loc. 336201, par. 9). Moses, Aaron, and Samuel, God's priests, guide God's people in worship of Christ, the true and eternal priest.
Verse eight speaks of the forgiving nature of God. Augustine notes, "God is not said to be forgiving toward anything but sins: when He pardoneth sins, then He forgiveth" (Augustine Psalms, loc. 336216, par. 9). Even when sins are punished, it is for correction, not to destroy. Augustine illustrates this with examples from the lives of Moses, Aaron, and Samuel, the three priests mentioned in the Psalm (Augustine Psalms, loc. 336221, par. 10). All humans sin and fail before God. He chastizes and restores them.
In the end, in verse nine, we are called again to magnify the Lord. Augustine reflects again on the ways we magnify God for his greatness. This, he says, is what brings all Christ's people together (Augustine Psalms, loc. 336255, par. 11).