John Calvin Commentary Psalms 72:6

"He will come down like rain upon the mown grass, As showers that water the earth." — Psalms 72:6 (ASV)

He shall descend as the rain upon the mown grass. This comparison may seem somewhat harsh at first sight; but it elegantly and aptly expresses the great advantage that all derive from the good and equitable constitution of a kingdom. We know that meadows are cut in the early summer when the heat is intense; and if the earth did not absorb new moisture from the falling rain, even the very roots of the grass would wither because of the soil's barren and parched condition.

Therefore, David teaches us that just as God defends the earth from the sun's heat by watering it, so he similarly provides for the welfare of his Church, and defends it under the king's government. But this prediction has received its highest fulfillment in Christ, who, by infusing his secret grace into the Church, makes her fruitful.