Exodus 9:25
And the hail smote throughout all the land of Egypt all that was in the field, both man and beast; and the hail smote every herb of the field, and brake every tree of the field. And the hail smote throughout all the land of Egypt all that was in the field, both man and beast; and the hail smote every herb of the field, and brake every tree of the field.
God first warned that the next day a hail more grievous than any since Egypt was founded would fall and kill every man and beast left in the field, testing Egyptian pride and revealing whose hearts had been affected by His dealings. That warning gave opportunity to bring servants and cattle indoors, and those who feared and heeded His word brought them into houses, while those who disregarded it and were hardened like Pharaoh left them exposed. When Moses stretched his rod toward heaven God sent the hail with thunder and fire mingled with the hail running along the ground, with lightning and storm.
The hail struck throughout all Egypt everything left in the open field, killing both people and animals, striking down every herb of the field, and breaking every tree of the field. Only in Goshen where Israel lived was there no hail, so the Israelites were spared. The flax and barley were ruined because barley was in the ear and flax was budded, but the wheat and rye were not ruined because they had not yet grown up.
The time of the plague was announced before it came, so it could not be said to have happened by chance. The plague demonstrated that the whole earth and its elements and forces of nature are under the command of the God of the Hebrews and that thunder, hail, and storm obey His voice. Those who heeded the warning escaped, showing mercy amid judgment and that safety lies in obeying God and that He protects His people.
Pharaoh, the proud king who had once questioned why he should obey the Lord's voice, was humbled to admit he had sinned, declare the Lord righteous and himself and his people wicked, and ask Moses to entreat God as his intercessor to stop the mighty thunder and hail, promising release. Moses answered that he would spread his hands outside the city so the thunder and hail would cease in order to teach that the earth belongs to the Lord, while declaring that Pharaoh and his servants would still not fear God. When the plague stopped Pharaoh refused to free Israel, as his continual opposition had hardened him until his whole being rose in rebellion against God's power.