The reader should note that from the beginning of the war “in the commencement of the twenty and fifth year” (Alma 51:1,12) to the end of Moroni’s war at the end of “the thirty and first year” (Alma 62:39) spanned seven years. This seven-year war had been won by Moroni and his people by means of oaths and covenants (see Alma 51--the title of liberty; Alma 53, 56--the sons of Helaman).
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]