I'm going to preface this by saying I'm not religious any more, although there are religious people and philosophies which I still deeply respect. I was born into a minority Christian sect which I am now estranged from.
Here's what I learned, when I was very young, about Shaitan (whom most of Christianity calls Satan). It was only considerably later that I began to question it, and discovered that it's not what everyone else learned. I don't know whether or not it is relevant to the current discussion, but it's at least an interesting view of the conflict between God and Satan that very few have heard.
Hum. I am completely unable to find this text in any computer-readable format anywhere. I guess I'll have to type it in.
At the very start of the Universe, God had his Angels to do His will. Angels are with no free will of their own, they exist to implement the will of God. Each Angel has a purpose, and must fulfill that purpose. Lacking free will, they cannot choose to do good, and God desired that beings free to choose otherwise should choose to do good, and he had a plan to create free-willed beings who could make that choice. Therefore many Angels had purposes which related to men.
One of these Angels, who was called the Morning Star, the Light Bringer, or Lucifer, has a very special purpose. He exists to tempt humankind to sin and divert them, if he can, from the path of righteousness.
The world, and people, were created as recounted in the book of Genesis, and unlike the Angels, they were given free will, because it is God's plan that they should be able to freely choose to do good. At the beginning, they were in harmony with God, but they were not good. They were not evil, but they were not yet good either, because although they had free will, they had made no choice to do good. And so Lucifer set to his appointed task, first drawing them away from their harmony with God in bringing them to eat the fruit of knowledge against God's order.
This was against God's order, but not against God's will. God intended for humans to know the difference between good and evil, so that they could choose one or the other. And that is why the tree of knowledge of good and evil had been first created. Not to eat the fruit of the tree was the one command God had given Adam and Eve, so Lucifer could not fulfill his purpose other than by making them to eat the fruit of the tree. This he did, as God had known he would and as God willed. The fall of man, the first sin, was what gave humanity the knowledge of good and evil, so that now men and women could choose freely between them with knowledge of which was which. Humanity was no longer in harmony with God, but was now capable of truly being good. Or, should their free will succumb to Lucifer's temptation, capable of truly being evil.
Because Lucifer's job was to tempt humanity away from choosing good, he always saw people at their worst. And because humanity, especially in those early days before the first purification of the flood, was weak, his job was all too easy. Yet, he saw that God valued the devotion of these weak creatures, humans, more than God valued the adoration of the Angels, because the Angels were not capable of making a free choice between good and evil. And so in his heart, Lucifer became jealous of man for God's love, and bitter at God for loving humanity more than the Angels.
It was this jealousy, this bitterness, that drove Lucifer to rebel against God. This was when he became known as Shaitan, or Satan, for he abandoned his angelic name as a sign of his rebellion. And he rebelled, by continuing to fulfill the purpose for which he had been created. Because he is an angel and angels have no free will, and he cannot turn from his purpose. His rebellion is not in his task, it is in his heart. He still does his task, but now he does not do it as other Angels do, with joy and love and devotion to God, but instead with resentment, and hate, and bitterness, and jealousy towards both man and God. He himself is the most tortured being in Hell, because he is an Angel who is no longer in harmony with God.
Shaitan sets the pattern for evil, because it is with resentment, and hate, and bitterness, and jealousy, that he brings men to sin. So be wary of these things, because when you feel them, they mean that Shaitan is with you, and you approach a point where a choice between good and evil must be made.