As the rain … and the snow. The rain and the snow are God's ministers (Psalms 148:8), and go forth from him, just as his word does. They have an appointed work to do, and do not return to him, whose ministers they are, until they have done it.
It is best to translate, with Delitzsch and Mr. Cheyne, "As the rain cometh down, and the snow from heaven, and returneth not thither, except it hath watered the earth," etc. The writer is, apparently, aware, as the writer of Ecclesiastes is, that the water which falls from heaven in the shape of rain does return thither again in the shape of vapour (see Ecclesiastes 1:7).