Augustine. Exposition on the Book of Psalms. Schaff, Philip (editor). New York: Christian Literature Publishing Col, 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 51, a penitential Psalm, speaks for the encouragement of the weak. Augustine sees that we rightly take it to apply to those Christians who have fallen into fear and have separated themselves from God’s people (Augustine Psalms, loc. 325376). Augustine observes that the sin of David with Bathsheba provided the occasion for this Psalm. While the fall of David is the occasion, the Psalm is more important because of the example of restoration (Augustine Psalms, loc. 325392). Augustine goes on to emphasize that the biblical command is that we should not be ruled by sin. Rather, we have an example of repentance (Augustine Psalms, loc. 325407).
Verse one calls out to God for mercy. Augustine sees this as indicative of a deep wound in David, who calls out to God as the great physician. His wound will not heal by itself (Augustine Psalms, loc. 325437). Augustine finds that the wound is so grievous because David didn’t sin in ignorance or by accident. He knew exactly what he was doing and how it was disobedient. For this reason, in verse two, he calls out to God for washing again and again, lest God should show justice rather than mercy (Augustine Psalms, loc. 325445). David’s sin is before him. It was even conftonted by Nathan the prophet. There was no reasonable excuse (Augustine Psalms, loc. 325453).
Commenting on verse four, Augustine asks why David would say he had sinned only against God? His response is that only God is without sin. Because of God’s justice our sin against him is more serious than any other aspects of sin (Augustine Psalms, loc. 325468). In contrast to God, David says in verse five that he was even conceived in sin. Though Augustine acknowledges that David was not born of adultery, he still lives out his life as a partaker of sin. He was never without sin, so he needed God’s mercy (Augustine Psalms, loc. 325484). In contrast, Augustine shows Jesus as the one born without the bondage of sin. The virgin birth, according to Augustine, breaks the power of the sinful nature, as he sees, based on Romans chapter 5, that the sinful nature is transmitted through Adam, the father. With the Holy Spirit as Jesus’ father, he didn’t inherit sin (Augustine Psalms, loc. 325499). For this reason, in verse six, David confesses that God can pardon hidden things. Augustine gives several examples of God overthrowing evil situations and building good ones. In the same way, in verse seven, David confesses that God can cleanse him with a humble hyssop plant, which, though it grew with little attention, was a strong medicinal plant (Augustine Psalms, loc. 325529).
In God’s work of cleansing, according to veses eight and nine, Augustine says God acts to turn his attention away from David’s sin. It is not David’s work, but God’s work (Augustine Psalms, loc. 325544). When God turns his face away from sin it is blotted out. Verse 10 then goes on to ask that God would rebuild David’s heart in righteousness. Again in verse 11, David asks for a corollary action. Not only should God not turn his face away, but David also doesn’t want to be cast out from God’s presence. Rather, he wants to have joy from God’s salvation restored. Augustine makes much of the fact that this is a restoration of what David once had (Augustine Psalms, loc. 325583).
David’s desire in his restoration, as stated in verse 13, is that he can teach God’s ways to unrighteous people (Augustine Psalms, loc. 325591). Augustine sees here David’s desire that people should be rescued from their sin, as they are delivered from the blood guilt of their sin (Augustine Psalms, loc. 325606).
In verse 15, David affirms the essential nature of confessing the praise of God. Our life of worship is not centered on sacrifice (v. 16). but on the praise of God. The true sacrifice we bring to God is our repentance (v. 17). Augustine notes that the necessary blood sacrifice is the one God has provided in Christ, to which all our offerings would reflect (Augustine Psalms, loc. 325622). The Psalm moves toward its conclusion speaking of God building his holy city and receiving our sacrifices of righteousness (v. 19). This is the conclusion, as we complete the pattern of repentance and trust, begun at the start of the Psalm.