Moses’ mortal life falls into three periods of about 40 years each.
First, from birth to age 40 in Egypt. He was reared as a prince and possible future pharaoh, learned in all the wisdom of Egypt. (Acts 7:22) It is said that he was also a city builder and successful military leader.
Second, from age 40 to 80, in Midian. Having fled for his life out of Egypt, he lived in the desert of Sinai, east of Egypt, as a tender of the flocks of Jethro, the high priest. He married Zipporah, daughter of Jethro, and she bore him at least two sons. Jethro ordained Moses to the Melchizedek Priesthood and no doubt taught him about the future Messiah. (D&C 84:6) It was while he was with the flocks, at about age 80, that the Lord called to Moses out of the burning bush, gave him a commandment to get the children of Israel out of Egypt, and revealed Himself to Moses as the great I Am.
Third, from age 80 to 120, in the wilderness of Sinai. After the burning bush experience, Moses returned to Egypt and with great exertion and the help of the Lord through 10 plagues, was able to get Israel out of Egypt and into the Sinai peninsula.
Two very dramatic events that occurred when he was about age 80, after the “burning bush,” were the passover of the angel of death who spared all those who had faith and put the blood of a lamp on the door posts, and the parting of the waters of the Red Sea, so Israel could leave Egypt.
It was during this period, between these two events, that Moses received the marvelous visions recorded in the book of Moses. (1:17-26)
. . . . . . . . . .
Moses led the children of Israel for 40 years, preparing them to cross over the Jordan River and enter the promised land of “milk and honey.” He was not allowed to enter with his people, which has been a source of misunderstanding. A few passages in the Bible seem to suggest that it was because the Lord was angry with Moses. (Num. 20:1-12; Deut. 3:24-28; 31:2) However, latter-day revelation enables us to see that Moses was translated. (Alma 45:19; D&C 84:25)
It hardly seems plausible that he would be denied entry into Canaan because of the Lord’s displeasure with him yet could be translated, which is a greater blessing. A better reason for Moses not entering Canaan is that the people did not deserve his leadership any longer. This is explained in D&C 84:20-25. He was translated so that he would have a body of flesh and bones so as to confer the keys of the priesthood, with Elijah (also a translated being) on the Mount of Transfiguration as told in Matthew 17. (Teachings of the Prophet Joseph Smith, p. 158) — Robert J. Matthews, “Moses: An Ancient Witness for Christ,” Church News, August 27, 1994, p. 12