What is the purpose of Satan in Christian theology?

Question: “What exactly is the purpose of Satan in Christian theology? Is he just a bogeyman type scare tactic? I ask because I remember being terrified on the bus in elementary school when an older girl told me all about Revelations, the anti-Christ, Satan, etc--this little Episcopalian had never heard any of that. And if he's not just something to scare waverers--if he represents an actual power that strives against God, then how is it a monotheistic religion?”

An Answer:

C.S. Lewis has a marvelous way of explaining the traditional view of the Devil/Satan for modern thinkers in his book Mere Christiantiy. Much of what I have to say here is inspired by his thoughts. Lewis points out that the concept of the Devil and Satan reveal several things about Christianity's view of existence:

‎1) God and the Devil are not equals. The philosophy that says good and evil are equal is called “dualism.” In dualism there is a never-ending struggle between good and evil and it is the opposition to the other that defines each. So a dualist would say, “We don’t know good times without the hard times.” The problem with dualism is that human existence is doomed to always know evil, wrong, and tragedy.  There is no possibility of existence without evil – a very grim forecast.

      The Christian view believes in a blissful paradise, an ideal state where good exists without evil. This is explained by the story of origin where good (God) exists before evil (the Devil). In short, the devil was the Archangel Lucifer, a created being who, though originally good, corrupted himself with envy, pride, malice, and self-deceit.  

Thus, Christianity teaches it is possible to have good without evil (God without the Devil) but evil without good cannot exist, just as Lucifer/the Devil would never have existed without God, his creator. The end result of which is that Christians don’t believe evil must exist, should exist, or will always exist. In other words, Christians have hope that evil will eventually not exist.   

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2) Evil cannot create. It can only corrupt.  Christianity believes that evil was never able to create, to make something from nothing. Evil can only take what is good and change it in some way God had not intended. There are several lessons here:

    - All created things are, by their original nature, good. There is nothing that exists that was ever   solely evil.

    - Many things that are good can be turned to evil. This is a warning against complacency. 

    - There is hope that anything evil might be turned back to good. This is called redemption.

    - If evil were ever successful in destroying good, evil would not be able to proliferate (since it cannot create) and would eventually die. Thus the end of evil is nihilism – self-destruction and non-existence.

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3) The names for evil specify its primary activity. The "Devil" means "deceiver" and "Satan" means "accuser". Thus in Job, the Satan is more like a lawyer making a case against Job. However, by the time of Revelation, Satan is in outright war with God, attempting to be Judge and Ruler of the world, accusing creation and God of abandoning each other. Revelation is the counter story, where neither God nor the People of God have abandoned one another. As the Deceiver, the Devil is attempting to convince God and Creation of the truth of a false reality – that neither loves, cares, or belongs to the other. 

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4) In continuing to teach about a "Devil" or "Satan", Christianity continues to assert that evil exists; can be recognized; is devious, cunning, adversarial, and even personal; and that we are currently in the middle of an epic conflict full of intention and not just random happenstance. Thus the Christian is likewise to be intentional in living life, carefully making choices and seeking God and not to naively or ignorantly stumble carelessly through life.

One last observation:  Our lives in the West are fairly shielded from some harsh realities - that's not to say life is easy here. I don’t mean that at all. What I do mean to say is that the idea of the Devil/Satan may look a lot more feasible to those of us in the world who have seen diabolical evil - millions injured or killed by plague, disaster, war, or genocide. 

In simple terms, without the Devil everything that happens, including tragedy, is a result of God's intention or negligence. Who else is left to attribute it to? And if God intends such tragedy, then we have to arrive at the conclusion that God is not supremely good.