Side note: I feel it is important to note when the word evil is used, it also refers to bad, as in bad thoughts, emotions, negativity etc.
Evil is a material construct. It´s main purpose being to create a balance within the material world. This balance of good and evil, light and dark is necessary as the primary learning tools for your life here on this planet.
You cannot know that something is good, without having a contrast, a comparison.
There is no evil in the spiritual realm, or heaven or whatever you wish to call it. It is not necessary there and it does not belong there. It has no place or purpose in the heavenly realms.
The material world is created by God, and therefore everything in it. Therefore evil is a tool that God has provided in order to make spiritual progress - our number one aim in this and each lifetime.
It is often hard, and understandably so, to comprehend that God could be the creator of evil. This is why man felt the need to create Satan or the devil - God´s alter ego, so that man could blame someone else for man´s misdeeds.
But the culprits unfortunately do not belong within the realm of God´s. The culprits are humans. Man himself was given choice. A choice to be good or bad. He creates the evil in the world, through his own desires, perceptions and emotions. Ego can also be a huge contributor to the perversion of one´s morals.
Look at nature - a pure reflection of the spiritual realm. There is no evil in nature. Everything works according to a natural law or instinct. Each animal hunts and kills in order to survive. No animal inflicts pain just for the sake of hurting another living entity.
The evil apparent around and within us is deeply linked to our karma. The hardships and difficulties we are exposed to are made apparent throughout our lives, as needed, to provide us with challenges to either fail, or overcome.
The frightening thing about evil is that it stagnates and it slowly permeates throughout one´s thoughts and then deeds, when left unchecked. We can look at someone who has committed atrocities and wonder how they could have reached such an evil mental state to actually carry out the perversions within their minds. This is not only stagnant, but living evil. When fed, evil begins to spread, sometimes without anyone even being aware of it. It is like a cancer, which eats away at the moral fabric of a person, a family or a community. Only when someone has the strength to fight against this with good, can such an evil be snuffed out. And do not fear. Good always prevails. It is just often hard to see and accept this.
Don´t forget that these earthbound lives are not always meant to be easy. We choose the paths we walk. We can choose the road less followed and stick to the truth in our hearts, which we all know. But evil is far easier. That is it´s nature. It appeals to our the senses, to the ego. It gives the illusion of power and grandeur and in some cases righteousness - such as atrocities committed in the name of God.
It is difficult to quell feelings of hatred and jealousy. This is the reason we are taught to master our minds and emotions so that when faced with the choice, we will always choose good over evil - even when it means sacrifice.
Beware in the modern age, of technology. There are plenty of ill meaning people who are more than willing to spread evil through technological means. Advertising, movies, news, etc, give a perverted mind access to millions of souls on a daily basis. Our children can be easily infected with images, ideas, and notions that get planted as seeds within their psyche. This is a new challenge of this age. It makes it harder than ever to overcome these base urges. The seeds are being planted while we are totally unaware. And it is usually whilst in an hypnotic state, making us even more susceptible. Should anyone wish to influence the masses it is very easy to do so.
Awareness is everything. We must make the choice not to accept or partake.
Shadow work is also very important. It is a means for us to understand and accept that we are all both light and shadow. We are all, as human beings, infected with our own dose of evil. This is dependant on karma from previous lives, actions we have taken, advancements we have or haven´t made. Shadow work helps us to confront this evil within us and to accept that it is a part of us.
Evil is human. Though it is easier to blame a devil, we cannot. When evil is left to fester without being checked, man is capable of anything.
Suffering is a tool. Heartache and heartbreak is a tool. Evil itself, is a tool. We can use it to strengthen ourselves against further perversion or suffering. We can use it to grow.
If you know the nature of evil you can reject it, learn from it or embrace it. That is our choice as humans.
That is the gift that we have been given.