I can see that you are at point zero where it comes to the Bible. I am not interested in taking you through a 20 year course on this. Some questions are OK, but a big involvement is not what I want to get into.
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I am going to answer this question, and then I'll look at the post and see what else I might take a swing at.
To answer this question, we begin in the garden of Eden.
The tree of knowledge of good and evil had little to do with knowledge. The point about it was the right of man to determine for himself what was good and evil. It was about obedience and rulership. Did Adam recognize the need to obey God in all things, or did he think that he could determine for himself (self rule) what was good for him and what was evil. In other words, did Adam want to obey God's theocracy.
When the being that became satan (meaning: adversary 'to God obviously') rebelled against God and got A&E to disobey, they chose his rule, do what you want rule. Satan never challenged the power of God. He challenged the right of God to rule man, the need of God to rule man. Since this was a question not of power, but of legalities, of what is just and right, the issue was a legal heavenly one.
In legal issues, you don't go blasting your opponent to pieces in a physical war, you go to court. In such a court evidence is presented and after the court is adjourned, a judgment is handed down. Since satan never challenged God's power, but only his legal right to rule man who was in God's image, God did not kill him. Instead, time was allotted to solve the court challenge.
For this reason, satan was also allowed what he needed to prove his point in this challenge to God. This is why he is called the ruler of this world. He is being permitted the time to prove that his rule, the rule of mankind according to their likes and dislikes, the personal choosing of what is good and evil, is going to benefit mankind, or not.
The issue has only been put to rest in our times of high tech. Even with our modern science, we are driving the earth into destruction, destroying the habitats and ecosystems, threatening to destroy all things with atomic warfare, with pollution, etc. And, we surely have proven ourselves incapable of handling our social problems, of assisting places, nations, on earth that suffer from famine, etc.
Since the legal issue is coming to its conclusion, the end of our world, not earth, is approaching. All national governments shall be erased and shall be replaced with God's theocracy with Christ as ruler.
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Thus about satan's power we read that he is the ruler of this world, that he has the power to cause death. He will gather all the nations in a final attempt of killing everyone on earth since he knows it is soon time for himself to die. It is the old style, 'if I can't have it, neither shall anyone else' philosophy. As you can see, the nations are getting ready for war, the doomsday clock is approaching 12 more than at any other time. As scripture says:
Revelation 11:17-18 . . .God, the Almighty, the One who is and who was, because you have taken your great power and begun ruling as king. 18 But the nations became wrathful, and your own wrath came, and the appointed time for the dead to be judged, and to give [their] reward to your slaves the prophets and to the holy ones and to those fearing your name, the small and the great, and to bring to ruin those ruining the earth.”
At no other time in mankind's history have we been bringing the earth to destruction, but we are now. Those who do so shall be erased, destroyed.
Please look beyond the first 30 seconds.
Basic info about advanced technology: Link: