It is quite clear on the one hand, particularly in the Psalms, that David and his dynasty are to be seen as God’s answer to the problem of evil. They will bring judgment and justice to the world. Their dominion will be from one sea to the other, from the River to the ends of the earth. And yet the writers all too aware of the puzzle and ambiguity of saying such a thing. The greatest royal psalm, Psalm 89, juxtaposed 37 verses of celebration of the wonderful things God will do through the Davidic king with 14 verses asking plaintively why it’s all gone wrong. The psalm then ends with a single verse blessing YHWH forever. That is the classic Old Testament picture. Here are the promises; here is the problem; God remains sovereign over the paradox. Split the psalm up either way, and you fail to catch the flavor of the entire corpus of biblical writing. God’s solution to the problem of evil, the establishment of the Davidic monarchy through which Israel will at last be the light to the nations, the bringer of justice to the world, comes already complete with a sense of puzzlement and failure, a sense that the plan isn’t working in the way that it should, that the only thing is to hold the spectacular promises in one hand and the messy reality in the other and praise YHWH anyway.
From N.T. Wright, Evil and the Justice of God, p.60.