This psalm expresses confidence in God’s steadfast love. In particular, it focuses on God’s covenant with David, whom He had exalted as king, and His faithfulness to David’s descendants forever.
The latter part of this psalm, which is not part of this Sunday’s reading, attempts to deal with the contrast between the blessing implied in that covenant with the reality the people are living. The psalmist recognizes that God may punish His people for forsaking His ways yet still keep His steadfast love for them.
But he goes on to express the anguish of those who have experienced the devastation of Jerusalem’s defeat and destruction by foreign enemies. In their great distress, can they continue to believe in God’s faithfulness? It seems that God has renounced the covenant.
Yet still the psalmist turns to God, asking for His blessing to return to the people, and ending with emphatic words of praise.
Hundreds of years after that psalm was written, centuries when the people of Israel continued to experience oppression by foreign rulers, a teenage girl receives a message that God is fulfilling that covenant. Her son will be the one to reign on David’s throne, and his kingdom will have no end.
This might have seemed doubly impossible to Mary, both because of the implausibility of her son defeating the might of the Roman empire, and because she could hardly have a son to begin with since she was unmarried and chaste. But the angelic messenger reminds her that God can do what seems impossible to us, and she responds in faithful submission to God’s will.
We can read in many places in the Bible about the prophecies made of a coming Messiah and the fulfillment of those prophecies in Christ. What is important is how we respond to these revelations, and Paul leads us in responding in obedient faith and enthusiastic praise.