Deuteronomy 31:20
For when I shall have brought them into the land which I sware unto their fathers, that floweth with milk and honey; and they shall have eaten and filled themselves, and waxen fat; then will they turn unto other gods, and serve them, and provoke me, and break my covenant.
God would bring Israel into the rich land He had sworn to their fathers, where after eating and filling themselves and growing fat they would turn to other gods and serve them, provoking Him and breaking His covenant. He warned them beforehand because He foreknew that prosperity in the promised land would not keep them faithful but would tempt them to turn away. He commanded Moses to teach this warning in a song that would stand as a witness against them when apostasy came and trouble followed. That song was to preserve the memory of His past dealings and His law, so families would teach it to their children, keep it in mind and heart through daily repetition and singing, and be safeguarded against forgetting Him.
Warning and Witness Song
When God would bring Israel into the land sworn to their fathers, flowing with milk and honey, and they would eat and fill themselves and grow fat, they would then turn to other gods and serve them and provoke Him and break His covenant. The enjoyment of abundance in that promised, fertile land would lead them to turn away after they had entered it and prospered and had enough. Prosperity there would not ensure faithfulness, for God foreknew their tendency to turn away after eating their fill and becoming prosperous. The warning was preserved in the song Moses was commanded to teach Israel so that it would stand and testify as a witness against them when this apostasy happened and when later troubles came upon them. That setting shows why families were to teach God's law plainly to their children and preserve it in their hearts so it would be known and obeyed and not forgotten, and why that history in song was to be remembered and taught to later generations as a reminder of God's past dealings and a safeguard against forgetting Him.
That song recounts God's past dealings with Israel and also prophesies future events, including the final victory of the faithful when Christ returns in power and glory. It was to be memorized and taught to children and sung in worship and repeated in daily work. The warning it carries was borne out in Israel's repeated disobedience, when they were scattered as captives and restored upon repentance and eventually overthrown along with Jerusalem.
Preserving Law Through Sacred Song
The commandments given around this warning were blessings and safeguards for the people, and preserving Israel's history in song made those records a reminder of God's past dealings and a safeguard against forgetting Him. The song Moses was commanded to teach would stand as a witness against them when, after enjoying abundance in the promised land, they turned to other gods, served them, provoked the Lord, and broke His covenant.
The warning shows why Israel's families needed clear instruction in God's purposes and requirements and were to teach God's law to their children and preserve it in their hearts. Those teachings were to be impressed on the people, including children, through repeated and engaging methods, so the law would be plainly known and obeyed and not forgotten. The song was compiled to teach God's commands and was sung during Israel's wilderness journey, reinforcing the need to teach children obedience and warning of the consequences of disobedience.
The law and its commandments were to be repeated in the wilderness and learned through solemn songs as the people traveled, which made God's will familiar and important to them. Israel was instructed to set the law to music and sing it while traveling, so its requirements would be firmly written in their minds and hearts. The song was to be memorized, taught to children, sung in worship, and repeated during daily work. Learning it step by step helped them keep pace as they traveled through the wilderness, and their orderly singing and marching taught respect and unselfishness. The verse's setting also keeps before the people that Christ was with them in the pillar of cloud and fire, and God's law was to guide their conduct as under Jesus' watchful eye.
God commanded Moses to preserve Israel's history and His dealings and lessons in a song with lasting memorials so its account could be remembered, kept in memory, and taught to children and later generations. The warning was preserved in a song so its account of God's dealings and its lessons could be remembered and taught to later generations, and sacred song can keep spiritual truth available to people when they later need it. Israel's enjoyment of abundance in the promised land carried the danger of turning from God. God promised rich provision, including the finest wheat and honey, if they kept His commandments and taught them diligently to their children, while disobedience would bring His displeasure.