Exodus 9-11

God has always been in a position that would permit him to destroy every evil doer. Maybe Moses had asked God why this stubborn pharaoh was allowed to live. Maybe the king of Egypt had challenged God's greatness by pointing to his continued life and rule over a faltering Egyptian empire. God helps us understand why evil people are allowed to live. In Exodus 9:15-16 God explains his mercy to pharaoh and Moses; so that they will see God's power and acknowledge who he is. Maybe that understanding would bring some evildoers into submission to God. God's love implies that such mercy  is worth the risk.
Stuart