Despite the similarities between the plagues, all of them had their own unique spin. Different plagues “attacked” different Egyptian deities, provoked different reactions, were manifested in different ways, or demonstrated control over various parts of nature.
But the hail plague was different in two enormous ways.
First, God put conditions on this plague that allowed some of the Egyptians to escape the punishment. Hail would certainly fall from the sky and kill off all the livestock, but it would only kill the animals that were left in the field. Egyptians who brought their livestock indoors would be spared.
Apparently, some Egyptians took Moses up on this, including those from Pharaoh’s own household. The Text says that they “hurried” to bring the animals indoors and were thus spared from this punishment.
Why did they do so? Because they “feared the Word of the Lord.”
That single statement puts their actions in league with the likes of Rahab, who saw the impending destruction of Jericho and actively took steps to avoid it. It also foreshadows the actions of Israelites who put blood on the doorposts to avoid the angel of death during the passover.
“Fearing the Word of the Lord” is what Pharaoh should’ve done seven plagues ago. Alas, this plague forces him to actually confess his sin before Moses, which is another reason this plague is unique.
To be frank, he doesn’t just confess his own sin, but the total righteousness of God, as well. (He also mentions the sinfulness of his own people, which seems like an unnecessary accusation when they had little to do with refusing Moses).
Unfortunately, by the time the plague is removed, Pharaoh’s heart is hardened again. But what this scene shows is that there’s a growing belief in the mood of the people—even those closest to him—that regards the word from Jehovah as important. And possibly, even higher than that of their Pharaoh.