Evil is classically defined as the absence or negation of good. It’s the lessening of or detracting from the goodness of anything. A broken arm is evil relative to a normal arm as the damaged arm’s purpose and function is impaired; it’s perfection has been compromised; it can no longer perfectly serve in its role as an arm. So evil is defined as the opposition or obstacle to achieving some perceived good. Evil has no reality of its own-apart from good, as everything in creation is good to begin with; nothing evil was created by God. Augustine put it this way, “The only possible source of evil, is good”.
Evil is a possibility due only to God’s giving part of His creation a particular good: free will, the abuse of which allows us to oppose* His* will. That opposition, itself, is sin, aka “moral evil”. In Eden Adam & Eve had no inclination to sin, no desire to rebel; the thought of murder or harming another wouldn’t even occur to them-and would be a complete anomaly in their world, a horrific one, if witnessed. Today it’s part of everyday life. We all know good and evil: the innate good of God’s creation, manifested in a myriad of ways, and the evil of sin, as well as the physical evils, pain, suffering, corruption, death-broken arms-that are said to be a consequence of man’s separation from God into this present exile away from Him, where not even faith- the knowledge of God-is sure. We’re lost… humankind is lost.
But there’s an upside. This knowledge of good and evil, that we experience morally, physically, viscerally, *directly *, has a purpose. By it, combined with an innate hope in something bigger and better and eternal, a hope that revealed and reveals Himself gradually to us as humankind becomes ready, we can come to know of our need for God, of his superior wisdom and goodness and trustworthiness, something Adam didn’t quite grasp, or something he rejected. The knowledge of good and evil can help us to learn the hard way, like prodigals, to appreciate and run to the Good alone. It’s a matter of the will-and God allowed the Fall to happen in order to *draw *our wills, and consequently ourselves, into perfection, aligned with His will, without coercion, having created His universe in a “state of journeying to perfection”, as the Church teaches. We can still always say no.