Is it important to have a testimony of the reality of Satan? Nephi was shown the doings of Satan many times throughout his vision. I think that it was important for Nephi to know the enemy that he was dealing with and would be dealing with. Nephi will later articulate the many devious ways of the Devil. In reading 2 Nephi 28, look back to what Nephi learned in 1 Nephi 12–14 about Satan’s tactics. Nephi knew the Enemy of all Righteous both by his vision and by his own experiences in life (See Figure).
Figure Welch, John W., and Greg Welch. "The Ways of the Devil." In Charting the Book of Mormon. Provo, UT: Foundation for Ancient Research and Mormon Studies, 1999.