Why is a fire prepared for Satan and his demons if they cannot be harmed by it? Many make the assumption, based on a misinterpretation of what Jesus taught in Luke 20, that angelic beings inherently have immortal life and CANNOT be put to death.
"And Jesus answered and said to them . . . But those who are accounted worthy to obtain that age . . . neither marry nor are given in marriage; And neither can they die any more, for they are equal to the angels" (verses 34-36)
In these few verses Jesus is only answering the Sadducees' question of marital status in the Kingdom of God. He is NOT addressing the question of eternal life or immortality. His primary point is that like angels who do not procreate, humans who are resurrected and changed into spirit will also not produce children. Those who are part of the first resurrection, which occurs when Jesus returns, are given immortal life as sons of God. They will have life inherently within themselves and never be able to die (see Hebrews 2:9:10, 1Timothy 6:12-16, etc.).
Angels are eternal. But they are NOT spirits that are immortal. Their life, as shown in many scriptures, can be ended by the One who gave it to them.
Fear of the angels
What is it that evil spirits know about God that would make them tremble in fear? This question is answered in Mark's account of Jesus meeting a man in a synagogue who was possessed with a demon.
"Now a man who had an unclean spirit was in the synagogue; and he cried out with a loud voice, saying . . . HAVE YOU COME TO DESTROY US? . . ." (Luke 4)
In verse 34 above the word destroy is a translation of the Greek word appolumi. This word, which is Strong's Concordance #G622, means to destroy fully and completely. This same word is also used to describe the utter destruction of people and places (Matthew 10:28, Luke 17:29, etc.). The question asked by the demon is instructive as it tells us something about their life and existence.
The Ultimate Punishment
After the millennial reign of Christ the devil will be permitted, for one last time, to active deceive others. After this last great evil act Lucifer, the angel who became God's chief adversary, will receive what he justly deserves for what he has done (Revelation 20:7 - 10).Lucifer will not, in spite of what some religious people might think, be tortured forever as his punishment. The Bible strongly indicates his life will be stopped - he will no longer exist AT ALL. He will be put out of his misery and his life terminated so that he no longer causes himself or others any problems.
Although Ezekiel chapter 28 seems to discuss a human king of Tyre, the description of his appearance and responsibilities CLEARLY point to it referring to the devil.
13 You lived in Eden, the garden of God . . . You had ornaments of gold. They were made for you on the day you were created. You lived on my holy mountain and walked among sparkling gems. 15 Your conduct was perfect from the day you were created until you began to do evil. ' (Ezekiel 28)
God also tells us through Ezekiel that Satan's destruction will be final and complete - he will not exist ANY MORE.
I will bring you to ashes upon the earth, before the eyes of all who see you. All who know you among the people shall be astonished at you; you became a terror, and YOU WILL NOT BE ANY MORE. (Ezekiel 28:18-19)
The devil will receive one of the worst penalties for his willfull sins - eternal death and separation from God (Romans 6:23) made possible by the Lake of Fire (Revelation 20:7-10).
The worst fate
For some evil spirits is there a fate WORSE than being dead forever? We receive a possible answer to this question when some demons say something to Jesus just before he casts them out of a person.
'What do You have to do with us, Jesus, the Son of God? Have You come here to TORMENT US . . . ?' (Matthew 8:29)
Notice that these demons greatly feared that a torment or torture would come to them before a certain time. What are these demented spirits talking about? The small book of Jude informs us of at least two kinds or types of punishment that demons will ultimately receive.
And the angels who did not keep their own original domain, but deserted their habitation, He is holding in eternal bonds under darkness . . . are themselves exhibited as a perpetual example of undergoing the punishment of eternal fire (Jude 5 - 7).
These verses show that at least some angels that turned demonic are restrained until they receive their punishment - eternal fire from God. Another set of rebellious spirits, however, will receive a slightly different fate.
wandering stars, for whom has been reserved the blackest darkness forever! (Jude 13).
It seems, from what little evidence the Bible offers, that some evil spirits will exist in the darkness of a prison forever - with no means of escape. God does not need to "do" anything special with such rebellious spirits, as their own sick and twisted minds become their punishment. And the devil, mercifully, will have his existence forever blotted out.