Satan wages war against the saints.

The Testimony of Joseph Smith

“I kneeled down and began to offer up the desires of my heart to God. I had scarcely done so, when immediately I was seized upon by some power which entirely overcame me, and had such an astonishing influence over me as to bind my tongue so that I could not speak. Thick darkness gathered around me, and it seemed to me for a time as if I were doomed to sudden destruction.

“But, exerting all my powers to call upon God to deliver me out of the power of this enemy which had seized upon me … I was ready to sink into despair and abandon myself to destruction—not to an imaginary ruin, but to the power of some actual being from the unseen world, who had such marvelous power as I had never before felt in any being…” (Joseph Smith History)

The Testimony of Zebedee Coltrin

[I] first saw the Prophet Joseph at a prayer meeting at the house of Father Morley. He was then a beardless young man. During the meeting the powers of darkness were made manifest in a remarkable degree, causing some to make horrid noises, and others to throw themselves violently around. One man by the name of Leman Copley, standing at the back side of the house was taken by a supernatural power, and thrown into the window. Then Joseph said to Lyman [Wight] “Go and cast the devil out of Leman.” He did so, and the devil entered into a brother by the name of Harvey Green and threw him upon the floor in convulsions. Then Joseph laid hands upon him and rebuked the spirit from him and from the house, upon which the spirit left him, and went outside among a crowd of men standing near the door and made a swath among them several feet wide, throwing them violently to the ground.