Students of comparative Christianity are well aware that many Christian churches today do not teach the actual existence of a devil. This condition was prophesied by Nephi wherein he stated that in the last days the devil would say to the people, “I am no devil, for there is none.” (2 Nephi 28:22.) The Book of Mormon and other latter-day scriptures clearly and definitely teach the existence of the devil as a personage of spirit. Concerning some of these teachings of the Church, James E. Talmage has written:
Now, I know that it is not quite in accord with the advanced thought of the day, according to certain cults, to believe that there is a devil, a personage, a reality. Many who pose as super-thinkers seek to dismiss, with the old ideas, the old stories, fables they call them, that form the bulk of the very word of God recorded as sacred writ, the fact of Satan’s existence.
But there is a personage known as Satan. Before he was cast out from heaven he was called Lucifer. He is just as truly a personage as are you or am I, though he is not embodied. He is in that unembodied state in which we existed prior to our birth into the flesh. And we read, as the Revelator tells us [Rev. 12:7-9], as Jude attests [Jude 6], that he was cast out from heaven because of his rebellion and all his angels or followers were cast out with him; numbering a third of the spirit-hosts of that particular class in heaven. (Rev. 12:4; D&C 29:36.] So they were many, and they are many …
Satan foresaw what would come to pass, and the prophet Nephi realized fully the claims that would be set up in the last days, these days. Read what goes before that which I shall read to you, and you will see that the prophet is referring to the time in which we live. He tells us that it will be necessary in this day that the kingdom of the devil shall shake, and he foretells that the devil will “rage in the hearts of the children of men, and stir them up to anger against that which is good.”
"And others will he pacify, and lull them away into carnal security, that they will say: All is well in Zion; yea, Zion prospereth, all is well—and thus the devil cheateth their souls, and leadeth them away carefully down to hell.
“And behold, others he flattereth away, and telleth them there is no hell; and he saith unto them: I am no devil, for there is none—and thus he whispereth in their ears, until he grasps them with his awful chains, from whence there is no deliverance.” (2 Nephi 28:21-22.) (Vitality of Mormonism [Boston: Richard G. Badger, 1919], pp. 123-24.)