Moses spoke with God face to face (Exo 33:11; Num 12:8; Deut 34:10). Deuteronomy is the result of this intimacy and the experience of forty years in the wilderness. Moses codifies and highlights what to him is most important in a well-known format that this new generation of Israelites would understand – a Hittite suzerainty treaty. This type of treaty was not used after 1200BC, a fact which supports Mosaic authorship. Moses writes Deuteronomy as a national constitution, a binding agreement between God and His people. Moses knows that his death is imminent.
Deuteronomy is Moses’ Farewell Address and the last book of the Torah or Pentateuch. The day after he finishes his swan song (literally – Deut 32!), one translation has it, according to J. Vernon McGee, that Moses “died by the kiss of God” (Deut 34:5-8) on his 120th birthday on Mount Nebo. God kissed Moses to sleep. What a lovely thought! Joshua, by this time around 80 years of age, probably authored Deut 34:5-12. Moses does not appear again until with Jesus on a different mountain – the Mount of Transfiguration in the Promised Land (Matthew 17:7).
The Mosaic authorship of Deuteronomy has been strongly attacked by critics who claim that Moses only originated the traditions which were later codified into Deuteronomy. These critics usually hold that this book was written by anonymous priests just before 621 BC and used by King Josiah for religious reform. However, Deuteronomy contains about forty internal claims to Mosaic authorship including direct statements by the book itself that Moses wrote it (Deut 1:1; 4:44; 29:1). Joshua also credits Moses as the author (Joshua 1:7).
The writing, geographical, and historical details all indicate a firsthand knowledge of the period between the Exodus and the Conquest of Canaan, not the time of Josiah over 800 years later. The rest of the OT attributes Deuteronomy and the rest of the Torah to Moses (Judges 1:20; 3:4; 1 Kings 2:3; 2 Kings 14:6; 2 Chronicles 25:4; Ezra 3:2; Nehemiah 1:7; Psalm 103:7; Daniel 9:11; Malachi 4:4). Deuteronomy is quoted in the NT over 80 times, the most of any book of the Pentateuch (Acts 3:22; Romans 10:19; 1 Corinthians 9:9).
Jesus Christ Himself credited Moses with Deuteronomy (Matthew 4:7, 10; 19:7-9; Mark 7:10; 12:19; Luke 20:28; John 5:45-47). George Mendenhall and Meredith Kline demonstrated that based on Late Bronze Age treaty documents found at Hattusas, the Hittite Empire capital, that Deuteronomy follows the standard international legal format used primarily in the fourteenth and fifteenth centuries BC – the Hittite suzerainty treaty. That is the time period of Moses.