My doctrine shall drop as the rain, my speech shall distil as the dew, as the small rain upon the tender herb, and as the showers upon the grass: Deuteronomy 32:2
Doctrine. Better, teaching, message or instruction; cf. Prov. 4: 2. The message conveyed by the Song shall, like rain and dew falling on plants, penetrate to the hearts of the Israelites; refresh, stimulate, and give birth to a new spiritual life. The Song, therefore, is not only one of warning, but on comfort also, to awaken new hope in a suffering Israel.
Distil as the dew. God’s word is as the dew which, though it falls gently and unheard, yet has a wonderful reviving power; cf. Micah 5: 6.
Small rain. The tender grass needs the small drops for its revival. Even so is the Divine teaching tempered to meet the wants of the weak and the young.
Showers upon the herb. The grown-up grass needs the strong forceful showers.
(Hertz, Dr. J.H., The Pentateuch and Haftorahs, 2nd Ed., Soncino Press, London, 1992, pg 896)