In verse 16, notice that in order for the purpose to be accomplished, it was necessary that man should be enticed by one or the other. I like that word entice; it’s a little different than the word tempt. We can be enticed by a lot of things and not all of them are bad in the sense that they come from Satan. Some things are better and other things are worse. One of the reasons that there is an opposition in all things is that we might be enticed—drawn to things—and because of that enticement, we can then make choices.
In verse 17, Lehi stated, "And I, Lehi, according to the things which I have read, must needs suppose that an angel of God, according to that which is written, had fallen from heaven." He is referring to the brass plates. Lehi had the plates of brass and he had studied them and in the plates of brass he learned that an angel of God had fallen from heaven and had become a devil, "for he sought that which was evil before God." What does that phrase mean? "To seek evil before God?" It may refer to the Council in Heaven when before God, meaning in the presence of God, Satan chose to rebel or to not adopt the plan of the Father, and because of that he became fallen. This is an important part of the Plan of Salvation.
Verse 18 reads, "And because he had fallen from heaven, and had become miserable forever, he sought also the misery of all mankind." Some people think that Lucifer’s misery is that he was cast out of the presence of God and cannot go back. No. He is not miserable because he cannot be with God; He opposes God and fights against him. His misery is not that he cannot be with God; his misery is that he can never become like God. He can never have a physical body, he can never be a husband, he can never have children, he can never have posterity. He is miserable because he is stopped in his progress. Satan is our adversary, a serpent, a father of lies, the evil one, the dragon, perdition, Beelzebub. He fights against God and does everything that he can to turn God’s children against God.
Book of Mormon Central, "Why Did Lehi ‘Suppose’ the Existence of Satan? (2 Nephi 24:12)," KnoWhy 43 (February 29, 2016).