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 affirms the pre-existence of Christ along with his unique identity as the God who takes on humanity, yet does it to redeem humans but not to deify them (Augustine Psalms, loc. 341741, par. 1). In Psalm 139:1, Augustine, taking the speaker to be Christ, notes that he refers to the Father as "Lord." This is not due to an inequality but due to Jesus' willingness to humble himself and take on humanity (Augustine Psalms, loc. 341746, par. 2). This immediately maks sense of verse two, where the sitting down would be in Christ's humiliation and the rising up would relate to the resurrection. Augustine also applies the concept to us, as we are penitent then receive forgiveness (Augustine Psalms, loc. 341756, par. 3). Verses 3-4 go on to observe that God knows all the journey of our life.
As verses 3-4 look forward in life, verse five projects our thoughts to the past. Augustine illustrates a past full of sins which called out for forgiveness (Augustine Psalms, loc. 341771, par. 5). Verse six then refers to the mighty work of God which could accomplish things. Augustine considers God's ability to speak through Moses as part of his mighty work, as it is something we could never accomplish ourselves (Augustine Psalms, loc. 341781, par. 6).
Verse seven asks where we could flee from God's presence. Augustine sees this as the question of an evildoer, such as a runaway slave (Augustine Psalms, loc. 341796, par. 7). God is present everywhere, so there is no escape from his presence. From heaven to Hades (v. 8), God is there. Verse nine further describes God as present, even over the sea (Augustine Psalms, loc. 341805, pr. 8).
Augustine finds a shift in attitude in verse nine. We formerly tried to flee from God's presence, but now we recognize that God was taking us wherever we went (Augustine Psalms, loc. 341810, par. 9). When we are ensnared, it is God who rescues us.
Verses 11-12 describe God as the one who brings light to darkness and who cannot be made dark himself. Augustine finds this as a crucial difference between God and sinful man, as evil people try to hide in darkness (Augustine Psalms, loc. 341825, par. 11). God changes that night to day.
In verse 13, God is the one who holds our reins, guiding us. In God's guidance we find delight, as he is the one who directs us well (Augustine Psalms, loc. 341840, par. 13). He does good works, which we confess freely (v. 14). In fact, we recognize (v. 15) that the Lord is even the one who makes our bones work as they do (Augustine Psalms, loc. 341850, par. 15). Augusitne also allegorizes the statement to refer to an inner strength of character.
Verse 16 speaks of God seeing us in our imperfectsion and making a written record. God knows the trials of his people, and knows what to do about them (Augustine Psalms, loc. 341871, par. 16). As a matter of hope, then, in verse 18, God will multiply those who were wandering about in the day he created. Augustine recognizes this verse as assuring us that God has a plan for the good of all his people (Augustine Psalms, loc. 341880, par. 17).
God's name and attitude is worthy of honor. Verse 21 speaks of the dedication the Psalmist has to the Lord (Augustine Psalms, loc. 341896, par. 18). God is the one who can govern the world in a consistent way, which Augustine recognizes as being done through God's Word and the Scracments. The Christian is able to reflect God's values rightly. The Psalmist asks for the ability to reflect God's attitude by asking, in verse 23, that God would test him (Augustine Psalms, loc. 341916, par. 19). As we are conformed into the image of God in Christ, we are better able to hold to the good fortune provide by God, as well as a proper reflection of God's people.