Following the “war in heaven” those spirits who remained loyal to our Father in Heaven earned for themselves the right to be born into this world and to receive mortal bodies of flesh and bone. Because of their loyalty to our Eternal Father, these faithful spirits had “kept their first estate,” pre-mortality, and thus proving themselves worthy for further advancement, had gained the right to enter into the “second estate” of mortality … It is important for us to remember that we are now here in mortality only because we “kept our first estate;” and that having proven ourselves worthy in pre-mortality of further “light and knowledge” we have been sent to earth to see if we will likewise succeed in proving ourselves faithful during this “second estate of our eternal existence.”
Because his [Satan’s] diabolical plan of “forced redemption” had been rejected by God and the righteous spirits present during the pre-mortal grand “Council in Heaven,” Satan and “a third part of the hosts of heaven,” who later joined him in his rebellion against God were eventually “cast down” to the earth as spirit entities—without the hope of ever gaining mortal bodies. Because these evil spirits recognized that without a mortal body and supremacy over the power of God they would be doomed to a state of eternal “non-progressive existence,” they sought to destroy what they thought was the intended designs, plans, and workings of God—hopeful that they could ultimately succeed in overthrowing our Father I Heaven, His power, and His works.
In our pre-mortal life each person who has lived, does live, or will live on this earth first existed as “intelligence” or “spirit element” and then secondly as “organized intelligences” or “spirit children” of our Father in Heaven.
Latter-day Saints hold it as common knowledge among themselves that every form of mortal life has had an existence before being born into this world. They call this “life before mortal life” the “pre-mortal existence,” the “pre-earthly existence,” or, as is often more simply but incorrectly expressed, the “pre-existence.”