But if thou refuse. God again urges him to obedience through fear of punishment, as He usually deals with the froward. Yet he permits him a short space of time for repentance, (as before,) if perchance he may lay aside his perverse determination to refuse. And this Moses now relates more distinctly in the fifth verse, both to show the extreme obstinacy of his malice, because the tyrant mocks at God's forbearance, and follows his own lust; and also to manifest more clearly from the circumstance of time, that the cattle of Egypt were smitten not by chance but by the hand of God. There is also an implied reproof of his senseless obstinacy, as though Moses said, that God was already enough, and more than enough, provoked; and therefore, unless he should desist, that God had new and more terrible plagues at hand, whereby He would overwhelm him. The murrain is appositely called God's "hand," because it arose from His just judgment; for this expression is opposed to natural causes, to the arts and devices of men, and to accidental chances -- as if Moses had said that the hand of God would appear in "the very grievous murrain," that Pharaoh may perceive the Deity to be wroth with him. Moreover, though this might seem a lighter plague than those preceding it, yet it was doubtless more grievous and afflictive to the Egyptians, because it involved much greater injury at a future period. The hand of God had before been adverse to them for a short time, and the evil had been removed together with the infliction; but now the destruction of the cattle will affect them for many years. For this kind of gradation in the judgments of God must be observed, as the Law also denounces against transgressors punishments sevenfold greater, if they do not speedily return into the way. (See Leviticus 26:18, 21, 24, 28.) As to his saying that "all the cattle died," it is a comprehensive expression, for immediately it will appear that a considerable number of animals still remained. But he means that the herds were everywhere destroyed, and the flocks smitten by the murrain; or, if you prefer it, that the murrain was general in its attack, and that it reduced Egypt to a state of poverty by the destruction of their cattle and other animals. Finally, the universal term merely refers to this plague having been a remarkable proof of God's anger, because the pestilence did not only kill a few animals, as it usually does, but made havoc far and wide of a vast number of herds and flocks.

For if thou refuse to let them go,.... Continue to refuse, as he had done:
and wilt hold them still; in the land, and under his dominion and oppression.