Why was Satan expelled from Heaven?
Satan was a cherub, one of God's most powerful angels, who openly rebels against God. Satan is jealous of God's omniscient status and pridefully wants to be exalted above God. Satan believes that he is God's equal and has the ambition to pursue his vain wishes. In a sense, Satan chooses to be expelled from heaven because he thinks "It is better to reign in Hell than to serve in Heaven." Satan's pride is responsible for his choice. He has faith in his own intellect above God's sovereignty and does not want to "serve" the Most High. Satan is content with attempting to ruin God's creation, humans, as a way to revenge his loss. In the book of Isaiah, Satan's intentions are described as it is written,
"For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north: I will ascend above the heights of the clouds; I will be like the most High."(Isaiah 14.13-14)
The anaphora "I" at the beginning of each verse reveals Satan's prideful nature. He is exclusively concerned with how he feels and believes he should be exalted instead of serving God. After Satan falls from Heaven with his band of angels who choose to follow him, he accepts his fate and does not repent.