Rain and snow fall from the sky and don't return without watering the ground. They cause the plants to sprout and grow, making seeds for the farmer and bread for the people.
The same thing is true of the words I speak. They will not return to me empty. They make the things happen that I want to happen, and they succeed in doing what I send them to do.
So you will go out with joy and be led out in peace. The mountains and hills will burst into song before you, and all the trees in the fields will clap their hands.