This psalm is titled "of Solomon" and was probably prayed at a coronation, and it opens as a request. 1"Give the king your justice, O God, and your righteousness to the royal son!" A king who asks for justice has already admitted that he cannot produce it himself. Whatever fairness his reign will show is a gift that must come from above.
The psalm then says what that justice looks like, and it looks like care for the powerless. 4"May he defend the cause of the poor of the people, give deliverance to the children of the needy, and crush the oppressor!" The test of a king here is his treatment of the people at the bottom, and the last verse of the test names the oppressor as an enemy to be crushed. A throne is measured by who gets heard in its courtroom.
The requests keep widening. 6"like rain that falls on the mown grass" is the picture of his reign. Justice, fruitfulness, and peace are never three separate wishes. They form a single hope, the wholeness the Old Testament calls shalom, running from a fair verdict to a field's abundance to a nation at rest. A king who rules as this psalm asks touches all of it at once.
Then the language outgrows the throne it was written for. 8"May he have dominion from sea to sea." No king of Israel, Solomon at his height included, ever ruled that far. The words are larger than any one man, and the psalm knows it. It is the kind of hope that every coronation carries, and it keeps pointing forward toward a king its writer could not yet name.
The center of the psalm is a portrait of mercy. 12"he delivers the needy when he calls," and 14"precious is their blood in his sight." Where other thrones celebrate themselves, this one is described by what it does for people who cannot repay it. Their lives are precious to him.
The blessing reaches back to Abraham. 17"all nations call him blessed!" The promise that all nations would be blessed through Abraham's offspring (Genesis 12:3) is folded into a prayer for one king's reign, so that throne and covenant become the same hope.
The psalm ends with two things stacked together. First comes a doxology, 19"Amen and Amen!" Then an editor adds a quiet note: 20"The prayers of David, the son of Jesse, are ended." A whole era closes in a sentence, the covenant handed from one king to the next, and the question hangs over the whole book of the Psalms: can a promise this large survive the handoff? No human throne could carry it to the end. One would, whose dominion does reach from sea to sea and whom the nations do call blessed. Until he comes in full, we pray this psalm for our own rulers and for ourselves, asking for justice we cannot manufacture and mercy toward the people nobody else is defending.
Prayer
Father, give every leader we live under the justice and righteousness that were always yours to give. Where the poor and needy have no helper, be their helper, and make their lives precious to those who hold power over them. We ask boldly for what this psalm always outgrew, a reign of peace to the ends of the earth, fulfilled in the one greater than Solomon whose name endures forever. In Jesus' name, amen.