The term "Deuteronomy" comes from Greek terms meaning "Second Law." Curiously, one of the Hebrew terms for this book is Mishneh Torah, which also means "Second Law." Mishneh Torah is also the term used for Maimonides' code of law and ethics. It took Maimonides (also called the Rambam) ten years to write this gigantic work. Mishneh Torah is also the term used for the copies of the Torah that kings are supposed to make for themselves in Deuteronomy 17:18. However, the normal Hebrew term for this book is Devarim, which is the second word of Deuteronomy 1:1, translated as "words." The -im ending makes it plural. Devar is the singular, meaning word or thing.
There are some modern Bible "scholars," such as the German School of Higher Criticism, who teach that Moses did not write the books of the Torah, (which includes the book of Deuteronomy. This is both blasphemous and anti-Semitic. This theory is an attack on the Jewish people, as well as an attack on Judaism. The very foundation of Judaism is the Torah. It should be noted that Torah more accurately means Instruction. However, the Greeks translated the term Torah with the Greek word Nomos, which means Law, and that term stuck in translations. There is much about law in the first five books of the Bible. However, most of the books of the Torah are not Law. We have the Creation, history, censuses, and some really great stories in these five books. These five books are also called the Pentateuch, from the Greek words penta, meaning "five," and teuchos, meaning vessel or container.
When I use the term Torah, I am usually referring to the first five books of the Bible written by Moshe (Moses). Many rabbis tend to do the same. However, many Orthodox rabbis will also include the entire Tanakh (OT), Talmud, Midrash, and various Rabbinic commentaries on the Pentateuch as being Torah.
Yeshua quotes Matthew 19:7-8, referring to Deuteronomy, and confirms that Moses wrote this book. In Matthew 4:4 and 4:7-10, Yeshua confirms this book as authoritative. I believe it is incumbent upon us as believers in Yeshua to also accept the books that Yeshua quoted as authoritative.
As mentioned earlier, Deuteronomy is also called the "Second Law." It is a summary of the past 40 years in the wilderness. It is basically a series of sermons and instructions given by Moses to the children of those who had left Egypt at the time of the Exodus. All of the men who were over the age of twenty had perished in the wilderness. Now their children were about to enter the Promised Land. "The entire Book of Deuteronomy was spoken by Moses in the last five weeks of his life." 
Up until this time, the Israelites had an almost constant awareness of God watching over them. They had heard of the miracles in Egypt that eventually resulted in them leaving Egypt. They were cared for in the wilderness with a constant supply of manna coming down from the sky each day. They had water coming out of a giant rock that followed them in their journey. Their clothing and sandals did not wear out. They had the supernatural cloud by day and pillar of fire by night that led them throughout their travels.
They are now a free people, no longer following the orders of the slave masters. However, they soon would be entering Canaan land. They would have to plow, plant, and harvest. They would have to establish courts of justice and government. They would need instructions on how to meet the needs of those who were less fortunate. They would need to avoid the temptations of the pagans of Canaan and to be aware of false prophets who might mislead them. And they would also have to fight their enemies. There is a time to be a pacifist, and there is a time to pass a fist.
Deuteronomy is not simply a review of the first four books of the Bible. There are about two hundred mitzvot (commandments) contained in this book (out of a total of 613), and seventy of these laws are completely new, not even mentioned in the first four books.
The word for wilderness is מדבּר (midbar). With different nikud (vowel markings), but the same consonants as above, it spells midaber, meaning speak. (There are no nikud in the original Hebrew.) The shoresh (root word) is דבּר (davar, meaning word or thing). This same root word is used for words meaning word, wilderness, and speak. God spoke to us, giving us His word, His mitzvot (commandments), in the wilderness, in a foreign land, not in Israel. God's Torah (instructions) are intended for both Jew and Gentile.