What is the difference between Good and Evil?

The only possible way that we can define good and evil is by introducing a deity. Without God there are no objective morals; we cannot say what is right and what is wrong. For a logical atheist, what is "good" and what is "evil" is rather arbitrary based on some notion passed down from society. We can only define good in this way: God is good and subsequently so is every law, commandment and word that He says. Anything that is not God or from God, is evil. When we are acting outside of God's will, we are acting "evil". Therefore, sin is "evil" and doing God's will is "good".