Why did God create Satan if He knew that Satan would sin?

Why did God create Satan if He knew that Satan would sin?

Firstly, God did know in advance that Satan would sin.  God has perfect foreknowledge.  He is omniscient or all-knowing. See Job 37:16; Psalm 139:2-4, 147:5; Proverbs 5:21; Isaiah 46:9-10; and 1 John 3:19-20.

The “why” part of the question is not directly answered in any particular Bible verse except that it is not always proper to ask the creator a “why” question.  

Romans 9:20  But who are you, O man, to answer back to God? Will what is molded say to its molder, "Why have you made me like this?"

However, when we seek to understand God rather than doubt him, we can explore the scriptures with an honest heart.  If God knew that Satan would sin against him, but created him anyway, then it follows that God must have planned to use the sin of Satan as a way to complete his will.

The fact that Satan sinned does not mean that God caused him to sin or that God wanted him to sin.  The Bible says that God does not cause sin (James 1:13).  However, God is able to take a bad situation and use it to fulfill his plans.  

Looking at how God will bring all things together under him at the end of time, it can be said that God will bring more glory to himself by saving and redeeming a lost human race than if he had just enjoyed a peaceful world for eternity.  The Lord redeemed mankind through the sacrifice at the cross, showing his generosity to undeserving sinners.  To Satan, he contrasts his actions, bringing only justice to Satan through condemnation.

The cross has always been the plan of God (Acts 2:23).  Christ himself spoke of the predetermined nature of his death (Matthew 20:28).  The cross is God’s way of making Satan’s rebellion and following fall of man into a blessing that lasts for eternity.