So who/what is the source of evil?
K
There are two lines of thought here, I think. Many Christian traditions equate the serpent in the garden with the devil, or a fallen evil angel like Satan possessing the body of a snake to deceive Eve. In this way, the source of evil is in both the temptation of the devil, and the succumbing to that temptation by Adam and Eve.
So it is not so much a source of evil, but sources of evil, the one in the devil carrying out evil intent, a spiritual evil, independent of mankind; the other is in the will of Adam and Eve that actively listens to the voice of evil, and actively choose the evil rather than good.
Pre-Christian traditions however consider the snake to be just that—a walking, talking snake, very cunning , but really bare-faced in his deception. Like all animals, the voice of God comes through his desires, and so what an amimal wants, an animal takes. It is in its nature, and God saw that that was good, as it had been stated previously after God created the animals.
For people though, the voice of God does not come to us through our instincts, but as a command to not eat the fruit of the garden. Eve had already heard that voice, either directly or through Adam more likely.so she knew that already. The snake simply pointed out that she probably really wanted that fruit, that is was desirable to her on every level, and she had to agree.
This is not as the evil inclination then, to listen to the voice of our desires over and above God's commands to us, and us alone. God wants us to be aware that we are of a higher spiritual nature than the animals, and that to act on the level of instinct and desire alone would in fact be evil for a creature such as us.
This insight is obviously true, whether or not God commanded Adam and Eve as he did, whether or not snakes could once walk and talk, or even whether or not the snake was somehow possessed of a higher order of evil in the guise of Satan.
For a world in which people went around acting according to their desires would be a world of psychopaths and narcissists, or maybe even more accurately, a world run by two year olds with adult strength and adult intelligence. What works for the animal kingdom would be disastrous for the world of men and women.
The source of evil for mankind then, biblically speaking, is acting according to our desires without consideration of what the voice that seeks order and goodness would be telling us is the better way.