1. Author and Time of Writing
Deuteronomy is the last book of the Pentateuch (Greek for "Fivebook") or of the Thora (Hebrew word for "law"). The unity of the Pentateuch and the fact that Moses is the author of it have often been denied since the 19th century. Criticism has especially focused on the book of Deuteronomy as it is said to have been written only at the time of Josiah, or even later.
Starting from 2 Timothy 3:16: "All scripture is given by inspiration of God" we can see in the Old as well as in the New Testament that Moses is considered to be the author of Deuteronomy and therefore the time of writing is confirmed. In Deuteronomy 31:9 and 24-26 it is testified that Moses wrote the book and that he gave it to the Levites to keep it. In Joshua 8:32-35 explicit reference is made to Deuteronomy 27:8-12 as "all that Moses the servant of the Lord had commanded before". While mentioning the law of Moses (Thora) in 2 Chron. 34:14 and Neh. 8:1 the book of Deuteronomy is included as well.
The Pharisees in the New Testament in Mat. 19:7 refer to Deuteronomy 24:1 with the words "Why did Moses then command...?" The Lord Jesus Himself confirms in the following verse that the command had been given by Moses. The following references of the NT mention Moses as author of Deuteronomy:
Sometimes the question is being raised as to who was the author of Deuteronomy 34 where we find the death and burial of Moses. It probably was Joshua, the friend and successor of Moses (Deuteronomy 34:9) who under the guidance and inspiration of the Holy Spirit added this short appendix to the whole work of his predecessor.
The events of Deuteronomy happen during the time of the first day of the eleventh month in the 40th year after the exodus out of Egypt (Deut. 1:3). The place of these events are the "plains of Moab" on the east side of Jordan.
2. Purpose of Writing
The name "Deuteronomy" for the fifth book of Moses means "second law". But the book is more than a simple repetition of the laws contained in Exodus, Leviticus and Numbers, which God had given the people of Israel at Mount Sinaļ. Out of the generation who were older than 20 years of age at the Exodus out of Egypt only Moses, Joshua and Caleb were still alive (Num. 14:29-30). Therefore a renewed repetition of the law for the whole people after such a long time was quite appropriate and necessary. But the main purpose of the book is the preparation of the people of Israel for the passage through Jordan and the entrance into the land of Canaan that had been promised by Jehovah.
The subject of Exodus and Leviticus was meeting God in His sanctuary. The purpose of Deuteronomy is the preparation of the people for the blessings, which Jehovah wanted to give them in the (promised) land. Obedience therefore plays an important part in this book. Obedience to God's laws brings blessing but disobedience will draw after curse and judgment.
In the New Testament the Epistle to the Philippians corresponds to the book of Deuteronomy. The people of Israel had been pointed to the blessings in Canaan while yet in the wilderness and similarly Paul was occupied with Christ the Lord in glory while still on earth.
a) In the New Testament we will find more than 30 verbal references out of Deuteronomy as well as many hints at facts that only occurred in this book. After the Psalms and the Prophet Isaiah Deuteronomy belongs to the most referred to books of the Old Testament.
b) The words "the place which the Lord your God shall choose" (for the place of worship) appears 21 times from chap. 12:5 onwards. This place was Jerusalem although the name of the city does not appear in the Pentateuch. Four hundred more years would have to pass until David and Solomon would find this place of worshiping God and would prepare it (1 Chron. 21:30 to 22:1; chap. 28).
c) When the Lord Jesus was tempted of the devil in the wilderness He three times replied: "It is written." (Mat. 4:4,7,10). Each time He refers to a verse of Deuteronomy (Deut. 8:3; 6:16; 6:13). These are divine proofs for the authenticity of Deuteronomy.
4. Overview of Contents
I. Deuteronomy 1-4: First (historical) Discourse of Moses
II. Deuteronomy 5-26: Second (legal) Discourse of Moses
III. Deuteronomy 27-30: Third (prophetical) Discourse of Moses
IV. Deuteronomy 31-34: Final Discourses and Death of Moses