Good appears to be embodied in being, in people for example. Goodness has a quality of a thing, something that exists in being. If evil is the opposite of good, then it too exists as a thing in being.
If evil exists as a thing, then God does not exist. Why? Because if God exists and is good, then evil cannot be created and exist, otherwise God is not good. In other words, if God creates evil then we are mistaken that the creator is all good and therefore we are mistaken about the creator-as-creator.
We have four possibilities: 1) God exists and has created evil (a contradiction and so we can dismiss this one); 2) God exists and has not created evil (although it can exist, just not as a created thing); 3) God does not exist (as monotheism describes God) and evil exists as a thing (as goodness exists as a thing). In this case we have a form of ancient Manichaeism which suggested a struggle between good (as a spiritual thing, but not with the attributes of the monotheistic God) and evil (as a material thing). Augustine of Hippo eventually came to dismiss this premise because this way of living condoned evil (after all, if it exists alongside good, and defines the physical world, it cannot be all that bad); or 4) neither exists.
So, the two premises with the fewest contrary or contradictory aspects are #2 and 4: God exists and evil is not a thing (a creation of a good creator), or God does not exist (with the attributes as outlines by monotheistic theology) and evil does not exist other than perhaps as an illusion.
We will develop point #2 and allow atheists/materialists to voice their view in #4.
If evil is not a thing, then what is it? Augustine of Hippo solved this problem (of whether or not evil exists) by arguing that evil exists as the absence of good. It is not an opposite thing to good. Instead it is the absence of that which is good. (We are not saying that people are evil. Instead, we are interested in evil as evil and not as embodied or not in persons.)
If evil exists, then, how does it continue to exist? How is it perpetuated? I think evil continues to exist as viruses continue to exist: Each has to seek a host on which to prey to continue in existence. In other words, evil must somehow (the mechanism of this need not concern us here) have an effect upon good so that it ceases to be good or at least fully good. It invades good, in a certain sense. (As a virus cannot be 100% effective in destroying all hosts lest it become extinguished, evil cannot be 100% effective lest it has no more hosts).
To continue to exist, a virus then needs to continually inhabit other hosts. Evil, then, must go from the goodness in one being to another being. Evil has to spread to continue in existence.
I think that resentment is a primary mechanism for evil to continually find new hosts in which to exist. Why? Because resentment is the seed of rage and revenge. If we can destroy the mechanism by which evil seeks new hosts, then evil is destroyed (because it no longer can jump from host to host, as a virus does.)
Forgiveness is the means by which resentment no longer exists. Forgiveness, therefore, destroys the pathway of evil from one person to another. Forgiveness stops the spread of the disease of evil as sound hygiene stops the spread of viruses.
Forgiveness not only provides the mechanism by which evil no longer can spread from host to host but also forgiveness stops the effects of evil within any one host (person). Forgiveness eradicates the resentment (with its concomitant anger, anxiety, depression, low self-esteem, and hopelessness) destroying the effects of evil.
Forgiveness, then, has a vital role to play in destroying both evil itself and the effects of evil.
Long live forgiveness. Is forgiveness a thing? We will ponder this one another time. Well, ok, here is the answer: Good exists as a thing. Forgiveness is part of the good. Therefore, forgiveness exists as a thing. If forgiveness exists as a thing, then what is it? From the viewpoint of monotheistic theology, it is an attribute of God and is therefore a thing. Atheists, you may come in with a different viewpoint, which we will respectfully consider.