Faith is not evil.

Faith in God is the key to decide to obey Him or not.  He reacts according to our faith.  Not obeying God is trusting the devil more than God.  It is going toward the evil instead of going toward the light.

People has always had a free will to choose between sin or not to sin.  We chose the evil path which was disobedience to God.

Evil is anything NOT GOOD.  

Evil can be explained in a simple way.  It is anything NOT holy.  It is anything on the dark side.  Dark is an eternal death.  If anything is not drawn to holiness, it is drawn towards unholiness or evil.  God is a God of light.  He exposes evil.