Elder Jeffrey R. Holland explains that goodness, holiness, and life would be dissolved in the absence of their opposites: wickedness, misery, and death. Opposition in all things brings illumination and meaning to the highest aspirations of mankind:
A related principle Lehi introduced as another backdrop to the eternal drama of the Fall and the Atonement is that of opposition, of contending enticements, a concept closely linked with choice and agency. If choice is to exist and agency is to have any meaning, alternatives must be presented. As Lehi phrased it, “It must needs be, that there is an opposition in all things.” [2 Nephi 2:11.] His reasoning and his vocabulary are clear and to the point. Righteousness has no meaning without the possibility of wickedness. Holiness would hold no delight unless we realized the pain of misery. Good could have no moral meaning if nothing could be considered bad. Even life—the nature and eternal possibilities of which are the subject of the plan of salvation and Lehi’s discourse about it—would have no meaning if we knew nothing of the nature and limitations of death.
In short, without opposites and alternatives, “there would have been no purpose in the … creation [of human life].” [2 Nephi 2:12.] All experiences in time and eternity would have been common, lifeless, indistinguishable—“a compound in one.” [2 Nephi 2:11.] At the end of this sequence would be the worst realization of all. There could be no happiness because there was no sorrow, and there could be no righteousness because there was no sin. But fortunately, there are happiness, righteousness, eternal life, and God, even as Lehi stresses that those blessings come only at the risk of confronting misery, wickedness, death, and the devil. (Christ and the New Covenant: The Messianic Message of the Book of Mormon [Salt Lake City: Deseret Book, 1997], 202)