Exodus 9:15
For now I will stretch out my hand, that I may smite thee and thy people with pestilence; and thou shalt be cut off from the earth. For now I will stretch out my hand, that I may smite thee and thy people with pestilence; and thou shalt be cut off from the earth.
This word was spoken as part of the judgments to secure Israel's release, as an early-morning warning before the hail demanding that Israel be let go to serve Him, so that Pharaoh might know there is none like God in all the earth. It declares that God could at once stretch out His hand and strike Pharaoh and his people, the Egyptians, with pestilence, so that they would be cut off and removed from the earth. Instead of destroying them at once, He let Pharaoh remain and preserved his life despite his crimes.
He raised Pharaoh up and used him and his stubborn resistance so that divine power would be shown through the judgments on Egypt and His name declared throughout all the earth, with the plagues that followed displaying His authority over the whole earth. He did not give Pharaoh life for this purpose; His providence placed Pharaoh on the throne at the appointed time. The death threat was followed by mercy giving time to gather cattle and all in the field into shelter before the grievous hail, and the hail, thunder, lightning, and storm obeyed His voice with their timing given beforehand so they could not be dismissed as chance.
Each plague was to be announced beforehand to give Pharaoh opportunity to respond, and rejected judgments would be followed by more severe ones until his exalted pride was humbled, testing the Egyptians and showing whose hearts were really affected by God's dealings with His despised people, until he acknowledged God as the true and living Creator. Pharaoh's refusal to let Israel go after the plague was stayed shows that continual opposition and repeated rejection of evidence hardens the whole being and makes the heart increasingly hard until it rises in rebellion against exhibitions of divine power.