As with all of God's higher beings, both men and angels, Satan was given free will because God desires true fellowship and not the orchestrated adoration of robots. We are told that, tragically, Satan used his free will to make a decision to rebel against God. Isaiah describes it in this way, quoting Satan (Isaiah 14:13-14):
I will ascend to heaven;
I will raise my throne about the stars of God,
And I will sit on the mount of assembly...
I will ascend above the heights of the clouds;
I will make myself like the Most High.
Notice the repetition of the phrase, "I will." The words literally seethe with rebellion. And Ezekiel tells us that the rebellion was rooted in pride: "Your heart was lifted up because of your beauty; you corrupted your wisdom by reason of your splendor" (Ezekiel 28:17). Satan became filled with unrighteousness and violence, and his sin resulted in God casting him out of Heaven (Ezekiel 28:15-17).
When was Satan kicked out of Heaven? We can only guess. The book of Job tells us that all the angelic host (which would include Satan) "shouted with joy" when God laid the foundation of the earth (Job 38:4-7). So Satan's fall must have taken place between the time the creation was finished and Adam and Eve were tempted. At the end of the creation week, God pronounced all of His creative work to be "very good" (Genesis 1:31), so the fall of Satan had to take place after that.
The gap between the end of the creation week and the temptation of Adam and Eve could have been anywhere between a few days or a few years. We know there was a lapse of time because Adam gave names to each of God's creatures before the temptation of Eve occurred (Genesis 2:19-20).
When Satan was cast out of Heaven, he took one-third of the heavenly host with him (Revelation 12:4). Jesus referred to this event when He told His disciples, "I saw Satan fall from Heaven like lightning" (Luke 10:18). The angels who rebelled with Satan became the demonic spirits that infest our planet today. This is the reason that Satan was referred to by the Pharisees as "the ruler of the demons" (Matthew 9:34).
In the next segment of this "Satan's Story" series, we'll look at what the Bible says concerning the vile characteristics of Satan.