Deuteronomy is the final book of Moses in the Old Testament. The events that occur in this book took place approximately forty years after the Lord brought the Israelites out of Egypt. Due to their lack of faith in the prior thirty-nine years, all the Israelites who were adults at the time they left Egypt died in the wilderness; all except for Moses, Joshua, and Caleb.
The word Deuteronomy means 'repetition of the law'. The book contains the three last discourses of Moses, which he delivered in the plains of Moab just before his death or translation. Moses knew that he would not enter the Promised Land with the rest of the people, but he was given the opportunity to instruct and counsel them before he left.
The book of Deuteronomy is called the second law because it contains Moses' summary of the Mosaic code. The first discourse found in chapters 1-4 is a 'remembering' of Israelite history. Moses told the people numerous times to remember or not forget certain important teachings that would help them to remain faithful.
The second discourse which is found in chapters 5-26 has two separate parts: 1) the Ten Commandments and a practical exposition of them, which is found in chapters 5-11 and, 2) a code of laws, which forms the basis of the entire book found in chapters 12-26. The first group of laws speaks of the ritual of religion and begins with a command to destroy all idolatrous objects of worship in Canaan; only one vital place for worship of Jehovah was acceptable. The group of laws dealing with administration of justice and the regulation of private and social rights finishing out these chapters.
The third discourse in chapters 27-30 contains a solemn renewal of the covenant and an announcement of the blessings of obedience and the curses upon disobedience; in chapters 30-34, an account of the delivery of the law to the Levites, Moses' song and last blessing, and the departure of Moses.
Because of its vital importance and the teachings therein, Deuteronomy is quoted over a hundred times in the New Testament.1
1 "Holy Bible", Bible Dictionary, Deuteronomy