Because our Heavenly Father chose Jesus Christ to be our Savior, Satan became angry and rebelled. There was war in heaven. Satan and his followers fought against Jesus Christ and His followers. The Savior’s followers “overcame [Satan] by the blood of the Lamb, and by the word of their testimony” (Revelation 12:11).
In this great rebellion, Satan and all the spirits who followed him were sent away from the presence of God and cast down from heaven. A third part of the hosts of heaven were punished for following Satan (see D&C 29:36). They were denied the right to receive mortal bodies.
Because we are here on earth and have mortal bodies, we know that we chose to follow Jesus Christ and our Heavenly Father. Satan and his followers are also on the earth, but as spirits. They have not forgotten who we are, and they are around us daily, tempting us and enticing us to do things that are not pleasing to our Heavenly Father. In our premortal life, we chose to follow Jesus Christ and accept God’s plan. We must continue to follow Jesus Christ here on earth. Only by following Him can we return to our heavenly home.