Why did Moses have to "stretch out his hand"?

"So I will stretch out my hand and strike Egypt with all the wonders that I will do in it; after that he will let you go." Exodus 3:20.

Obviously this is God speaking - so I guess my question as I was reading this morning is why does God ask Moses to  "stretch out your hand".  At least 10 times God asks Moses to stretch out his hand before God does something amazing - frogs, water to blood, hail...  Whatever He is about to do - he precedes it with Moses stretching out his hand.

God does not need Moses to do anything - He already had the plan - He already stated that He was going to stretch out HIS hand and strike Egypt.  So why did Moses have to stretch out his hand?

At first glance, it seems that maybe obedience is the issue.  Moses shows his obedience to God's command and God acts.  That could be it.  

But as I thought about it, I think maybe it is God using Moses as a physical representation of Himself to the people and Pharoah, so when they see Moses, they can "see" God stretching out His hand.

As I thought about this - my thought was - how do I reflect God to the world around me?  As I move, as I speak, as I act, how does the world perceive God?  I realize I am not given specific instructions like Moses was - but I have been given guidelines that help me reflect Christ in the world.

Today, as I stretch out my hand, it is my desire that others see God clearly.  God help me represent you well to the world around me.