John Calvin Commentary Exodus 9:18

"Behold, to-morrow about this time I will cause it to rain a very grievous hail, such as hath not been in Egypt since the day it was founded even until now." — Exodus 9:18 (ASV)

Behold, tomorrow about this time. God now indicates the kind of punishment He was prepared to inflict, namely, that He would smite with hail both man and beast, and a part of the crops.

It sometimes, indeed, happens that grain is destroyed by hail, and occasionally great injury is thus inflicted even on men and beasts. In fact, it is regarded as an unusual blessing if ten or fifteen years pass by without such a calamity.

But God makes it clear by certain signs in the judgment He has determined to execute that the hail did not arise from natural causes, but that the atmosphere was manifestly armed by Him for the battle.

First, tomorrow is fixed; nor is this enough, the hour also is added. But what astronomer or philosopher could thus measure the moments for storms and tempests? Then again, its unusual violence, such as had never been seen before, is specified. Fourthly, its extent: from the extreme boundaries of Egypt, from one side to the other, as well as its expansion over its whole breadth. Scarcely once in twenty years will a storm prevail so widely, flying, as this did, like an arrow; but, restrained within narrow limits, it will not thus diffuse itself far and wide. Lastly, the distinction is added between Goshen and the rest of Egypt.

Therefore, it is plain that this hail was not produced by an accidental impulse but was made to fall by God’s hand. In a word, it was not the drops of moisture frozen in mid-air, but a portent that transcended the bounds of nature.