I. The Jew was to understand from his first entry into the land of Canaan that his prosperity depended utterly on God. The laws of weather, by which the rain comes up off the sea, were unknown to him. They are all but unknown to us now. But they were known to God. Not a drop could fall without His providence and will; therefore they were utterly in His power.
The warning of this text came true. More than once we read of drought, long, severe, and ruinous. In one famous case, there was no rain for three years, and Ahab had to go out to search through the land for a scrap of pasture. These droughts came at times when the Jews had fallen into idolatry and profligacy.
II. It is the intense faith in the living God which can come only by the inspiration of the Spirit of God which proves the Old Testament to be truly inspired. In later times the Jews had these words of Moses written on their foreheads, but not on their hearts. They had lost all faith in God; He had spoken to their fathers, but they could not believe that He was speaking to them, not even when He spoke by His only-begotten Son, the brightness of His glory and the express image of His person. Wrapped up in their narrow, shallow book-divinity, they said, "This people who knoweth not the law is accursed." Nothing new could be true. It must be put down, persecuted down, lest the Romans should come and take away their place and nation. But they did not succeed. The Romans came after all and took away their place and nation, and so they failed, as all will fail, who will not believe in God. The truth which they think they have stifled will rise again, for Christ, who is the Truth, will raise it again, and it shall conquer, and leaven the hearts of men till all be leavened.
C. Kingsley, Gospel of the Pentateuch,p. 210.
References: Deuteronomy 11:12. Spurgeon, Sermons,vol. xiii., p. 728. Deuteronomy 11:18. H. Melvill, Penny Pulpit,No. 2580. Deuteronomy 11:18-21. H. W. Beecher, Christian World Pulpit,vol. xviii., p. 152.