From An Opinionated Dictionary of Religion at uponreligion.com
DEVIL. Noun. A felon on license from God to wreak havoc on Earth.
The notion that unfortunate events are caused by unseen evil entities is prehistoric and ubiquitous. Every tribe has had its dastardly creatures responsibly for bad luck.
Each culture's pantheon of gods includes deities who did the dirty work of disease and possession and war and panic.
It wasn't until the ancient Persians divided the world into the two warring sides of good and evil that one all-good God and one all-evil God were conceived. And it was the all-evil God who morphed into our devil via the ancient Jews in Persian captivity.
The ancient Hebrews attributed all evil events to God until they encountered the Persians. Before Persian influence, Isaiah could say--somewhere in Chapter 45--that God was responsible for good and evil. But over time, with the Persian stimulus, the biblical God became a God of 'loving kindness,' and evil was pushed off on to others.
So, where did evil come from, if not from God? Jewish thinkers, writing after most of the Hebrew biblical books were composed, concocted the mythology of the fall of the rebel angels in books like Jubilees, Watchers, and others. Evil came from the rebel angels, not from God.
These writers capitalized a common Hebrew word for 'adversary'--satan--and turned that word into a name for the leader of the fallen angels. Various motives caused the fall of Satan, according to varied non-biblical books that constructed the devil's biography: the devil's envy of God, the devil's injured pride, the devil's ambition.
Jewish writers of the devil mythos projected the devil back into the Hebrew Bible where he never was--as the snake in Genesis and as the adversary in the book of Job.
Subsequently, Jewish sages recognized this literary subterfuge and rejected these books and the devil with them.
All this devil lore in post-biblical Jewish literature so influenced emerging Christianity in the first century that the earliest writers of Christian literature were simply able to mentioned Satan without explanatory introduction and the hearers and readers knew the character. They already knew Satan's biography. And the only way they knew it was through post-biblical Jewish literature like the book of Jubilees and the book of Watchers.
This Hebrew word--satan or adversary--was translated into ancient Greek as diabolos, again 'adversary,' and from there it's easy to see the connection to similar words as they and from there it is easy to see it appear in Romance languages, as well as in the English word devil.
The devil idea is supposed to exonerate God from complicity in evil, and it could do that in ancient Persian dualism, where the God of good and the God of evil are equally powerful.
But in Western theism God is said to be all-powerful. The devil is not more powerful or even as powerful as God, and so, God could stop the mayhem of the devil. But no. God doesn't stop the weaker devil.
So, it seems that by permitting the devil to perform and perfect his evil deeds God does assume some responsibility for evil. We humans don't let known killers roam free if we can catch and jail them. But God lets the devil roam free. And so, the devil idea does not exonerate God from complicity in evil.
That's a pretty good strike against the devil idea.
What is more, the devil idea has had very real deleterious effects in the world; it actually caused the very thing it purported to identify: it caused evil.
All the alleged enemies of Christianity--Jews, pagans, Muslims, unbelievers, heretics, apostates, infidels, 'witches' and 'savages'--were all defamed as 'servants of Satan' and duly punished for the association. The three-century-long European Witchcraze (aptly called a satanic panic) killed tens of thousands of innocent girls and women, suspecting them to be in collusion and sexual commerce with the devil to bring down Christian civilization.
There were no witches. And there was no devil.
If you search out the iconography of Satan from the sixth century to the present, you will see that artistic renderings of the devil evolve from the horrific to the heroic to the hilarious. That change directly reflects the degree to which the devil idea is believed over the centuries. Deep belief in the devil paints him hideous and scary. But by the nineteenth century a tapering belief could lead William Blake to paint a heroic devil standing beautiful and bold against the odds, rather reigning in hell than serving in heaven. And by the late twentieth and early twenty-first centuries, painters paint a silly devil, a comic character, a used car salesman with stubby horns, an aproned backyard bourgeoisie toasting souls on hibachi grills, an afternoon drunk sunk in a sofa eyeing soaps.
The devil idea is unworthy of assent. The devil idea is itself demonic. It is an idea with corpses in its wake. And nowadays it's more laughable than laudable. Be gone, Satan! Be gone!