That one decision opened a door that should have stayed closed. Each of us face temptation every day. We must remember that it never comes from God. The ability to resist temptation is of God but the temptation itself is always from the devil. In the context of the actions which these characters have taken, it is a chilling question.
Evil is a spiritual reality that can have a physical presence.
It is not something that any of us ever want to feel. If evil is within us, the power of God is not. They cannot coexist. God is all light. Evil is pure darkness.