Shevat is the 11th month of the Biblical calendar. Because the Roman or Gregorian calendar is the one in standard use today, the day shifts around each year, and we miss the significance of a date when spring actually starts, since the Roman calendar is not based on seasons.
On Shevat 1 or around January 20, B.C. 1407, Moses began teaching and presenting the book of Deuteronomy for the 40 days before his passing. He had given the book of Exodus both verbally and in written form about 38 years earlier. Now that generation had died off, and the younger generation needed to hear the instructions and commands of God before entering the Promised Land.
Deuteronomy 1:1-5 These be the words which Moses spake unto all Israel on this side Jordan in the wilderness, in the plain over against the Red sea, between Paran, and Tophel, and Laban, and Hazeroth, and Dizahab. (There are eleven days’ journey from Horeb by the way of mount Seir unto Kadeshbarnea.) And it came to pass in the fortieth year, in the eleventh month, on the first day of the month, that Moses spake unto the children of Israel, according unto all that the LORD had given him in commandment unto them; After he had slain Sihon the king of the Amorites, which dwelt in Heshbon, and Og the king of Bashan, which dwelt at Astaroth in Edrei: On this side Jordan, in the land of Moab, began Moses to declare this law, saying,
During these 40 days, Moses spoke to the entire nation, after having defeated the kings on the East side of Jordan. He went over the Law, gave a history of the nation, prophesied of the future of Israel, and gave blessings to each tribe. He also made 13 copies of the Torah scrolls, so each tribe would have their own copy and the Ark housed one as well.
Moses at this point was 120 years old and yet had not aged for many years.
Deuteronomy 34:7 And Moses was an hundred and twenty years old when he died: his eye was not dim, nor his natural force abated.
It was time however for Moses to go. God had set this age as the limit man was to live on the earth. So God took Moses to the top of a mountain and let him view the Promised Land, before secretly burying him.