According to McConkie and Parry, the root of the Hebrew word for seven (sheva) is identical to the Hebrew verb that means “to take an oath,” thus connecting the word seven to covenants and covenant making. Further, the word seven denotes perfection and completion. [Joseph Fielding McConkie & Donald W. Parry, A Guide to Scriptural Symbols, p. 99]
“Having Reserved for Themselves Provisions for the Space of Seven Years”
According to Hugh Nibley, the Nephite governor Lachoneus “sent a proclamation among all the people, that they should gather together their women, and their children, their flocks and their herds, and all their substance, save it were their land, unto one place” (3 Nephi 3:13). The order was quickly and efficiently carried out with incredible speed, the people “coming forth by thousands and by tens of thousands … to the place which had been appointed” (3 Nephi 3:22). The people were used to such gatherings. Particularly significant is it that they brought with them “provisions … of every kind, that they might subsist for the space of seven years …” (3 Nephi 4:4), since as Dr. Gordon has shown, the purpose of the Great Assembly in ancient Palestine had always been to insure a seven-year food-supply, rather than an annual prosperity. (C. Gordon, Ugaritic Literature, pp. 4-5). [Hugh Nibley, An Approach to the Book of Mormon, (1957), p. 268.]
According to Nibley, seven years was a set policy of ancient times--the seven-year cycle. You know, the seven lean years and the seven fat years [in the story about Joseph in Egypt]… . You would get enough food for seven years, and this was a law in Israel too. Remember, every seven years was a year of release, the Lord’s year. The year of release was the seventh year, and the great year was the seven times seventh year, the 49th. So they were just following the old Jewish custom of getting all the stuff you’d need together for a seven-year cycle. [Hugh W. Nibley, Teachings of the Book of Mormon, Semester 3, p. 301]