Why did not God destroy Satan promptly after he rebelled?

You will find your answer in the 76 section of the Doctrine and Covenants (google; D&C) In a nutshell, all people are spirit children (Hosts of Heaven) of God and were sent to earth to earth to gain a physical body and to carry out a Plan of salvation. Christ said he would make laws known and would pay for the sins of those who repent (change their ways) or they would have to pay for their own sins and receive a lesser kingdom at judgment day, but all would be saved and He would give God the glory. Satan said he would force obedience and would be above God. Christ was chosen, so Satan and a third of the Hosts of Heaven were sent down to earth for rebellion to become the Devil and his angels. They would like your body, but a swine will do. Opposition is necessary.