It is clear from the second half of the psalm that Ethan the Ezrahite is perplexed about why God seems to have rejected his people. His perplexity is not caused by the fact that they deserved to be punished for their sin. Instead he is puzzled because it seems that God is not keeping his promises to ensure that there will always be a king on the throne of Israel who will be descended from David.
In verses 1-4, Ethan praises God for making that commitment to David and his seed. This commitment was made after the Lord had done many other great things for his people, especially at the Exodus when he made a path through the Red sea and defeated the power of Egypt (vv. 9-10), and then when he gave to them the Promised Land (v. 12) and protected them from their enemies (vv. 15-18). God had shown himself faithful to his promises when he did those great things for his people and Ethan calls on the angels to join him in praising the Lord for such displays of power (vv. 5-8).
The climax of the Lord’s goodness to Israel was to choose David as their king. Ethan recounts the various promises that God had made to David and his descendants (vv. 19-37). In fact, supreme earthly authority was promised to David (v. 27), and not even the sins of his descendants would prevent the endless nature of his dynasty (vv. 29-37). Yet, as Ethan looked round, he could see no indication that God had kept his promises about David’s royal line. In fact, the opposite seemed to be the case.
Ethan feels deeply the visible demise of God’s kingdom. Yet he knows that the Lord has the power to change the situation and restore his kingdom. So he asks the Lord to answer his prayer for restoration, and to do so within his own lifetime (vv. 46-48). His only hope in his dismal surroundings, made worse by the derision of their enemies, is still the covenant promises that the Lord made to David about his royal line.
What does the theme of the psalm have to do with us who live in the New Testament period? We have more knowledge that Ethan had because we live after the coming of the Messiah. We know that the Lord has kept his promise about the universal and endless reign of the descendants of David – he has given the place of permanent and complete power to Jesus when he ascended to heaven. What Ethan longed to see, we now know has taken place. We can sing this psalm knowing that, in the Lord Jesus, God has kept his promises to David and done so in a manner that has far exceeded the expectations of his harassed servant Ethan.
Since the Father has kept his promise to give an eternal throne to the Descendant of David, we can expect him to keep all the other promises he has made in connection to that kingdom. How delighted we should be that we live under the actual rule of the God-man, Jesus, the ongoing fulfiller of the promises made long ago by his Father to David.