Exodus 9:13 & 14

"Then the Lord said to Moses, 'Get up early in the morning, confront Pharaoh and say to Him, "This is what the Lord, the God of the Hebrews, says: Let my people go, so that they may worship me, or this time I will send the full force of my plagues against you and against your officials and your people, so you may know that there is no one like me in all the earth."'" NIV translation

Pharaoh is given another warning but this one is much stronger. With all that they had seen, it is hard to imagine what the "full force" would have meant to them. God says that the purpose of these plagues is so that Pharaoh and all the others could see that there was no one like Him. They were used to having all sorts of gods but were being put on notice that there was none other than God.

Exodus 9:15 & 16

"'"For by now I could have stretched out my hand and struck you and your people with a plague that would have wiped you off the earth. But I have raised you up for this very purpose, that I might show you my power and that my name might be proclaimed in all the earth."'" NIV translation

Pharaoh is reminded of the fact that God could have destroyed him and his people with a single act. Instead, He has used them as a demonstration of His power to glorify His name. 

The same thing is true for us before we accept Jesus Christ. God would have been just to wipe us off the earth but He demonstrates His mercy to Glorify His name.