From a philosophical perspective, the universal belief in Satan and evil demons is based on the need for an explanation of the enormous quantity of moral and physical evil pervading human existence for our entire history. The manifest presence of suffering in the lives of all is a fact which cannot be ignored nor denied. As the search for meaning in existence inevitably develops, explanatory systems emerge to cope with fundamental existential questions.
One response is the postulation of the existence of a being or beings who create and/or personify evil. While the figure of the Christian Devil, Satan, most clearly exemplifies the anthropomorphic concept of evil, there are numerous examples of gods or spirits from widely divergent cultures who share some of his most prominent characteristics. This shows that the concept of "the Devil" far from being a phenomenon with origins specific to Christianity, can be found in various forms throughout history, regardless of time and place.
Psychologically, demons may well be a projection of ourselves, the worst part of our nature or the most feared part of our own nature.
If Satan were merely a personification that people have devised to express their ideas of evil, then such a personification could scarcely be held morally responsible for his actions, since, in reality, there is no being who can be held accountable. But Satan is held accountable by the Lord (Matt. 25:41), and this passage reminds us that to deny the reality of Satan requires denying the veracity of Christ’s words.
Some argue that part of the reason for man’s creation and for God’s plan of salvation in Christ is to demonstrate the truth of God’s character as wise, holy, just, loving, gracious, merciful, and good. To reveal God’s glory, Satan was created as the shining one, the morning star, and, having foreknowledge of what Satan would do, God elected to create Satan and to use the blackness of his sin to reveal his divine essence only more emphatically. What is it that makes the stars shine at night? It is the darkness.
In his holiness and justice, God had no other choice but to judge Satan and his angels to the lake of fire and the same is true with sinful man. But being also merciful, gracious, and loving, he provided a solution through the cross so that man could regain eternal life. This gracious plan of love was not only anticipated in the Old Testament, but was actually first announced to the serpent (the devil in disguise) in Genesis 3:16, which is significant in view of the angelic conflict and the slanderous accusations of Satan. God is sovereign and even though the creature rebels no one, neither Satan nor man, can thwart the purposes of God. In the outworking of God’s wisdom and power, having given all the angels volition, he allowed Satan to sin and uses him as a catalyst to promote his glory.
Some believe that God created Satan to be evil and to fulfill a specific purpose here on the earth as the adversary and tempter of mankind. Those who teach this doctrine primarily cite two Scriptures in support of their position: Isaiah 45:7 and John 8:44.
“I form the light, and create darkness: I make peace, and create
evil’” Isaiah 45:7
"You are of your father the devil, and the desires of your father you want to do. He was a murderer from the beginning, and does not stand in the truth, because there is no truth in him. When he speaks a lie, he speaks from his own resources, for he is a liar and the father of it."John 8:44
It must be emphasized that belief in Satan as an external spirit does not excuse us from responsibility for our sins or false beliefs. We cannot blame Satan for our errors, claiming that “the Devil made me do it.” We are responsible for learning the Truth, and turning from our sinful ways. The temptation which arises from the heart of man and the evil thoughts which proceed “from within, out of the heart of man” (Mark 7:21) may be prompted by Satan; they may also arise naturally, since human nature has been poisoned by the disobedience of Adam and Eve. But we must not confuse the evil which comes “from within, out of the heart” with the Satan who comes up from the outside, as in the temptation story. There is a close connection between sin and the original cause of sin, just as the conductor and the music he produces from an orchestra are connected. But no one would confuse the conductor with the orchestra.