Exodus 8:13
And the LORD did according to the word of Moses; and the frogs died out of the houses, out of the villages, and out of the fields. And the LORD did according to the word of Moses; and the frogs died out of the houses, out of the villages, and out of the fields.
The Nile sent the frogs across the land as a nuisance and torment, and they died throughout Egypt, out of the houses, out of the villages, and out of the fields where they were. The Lord removed and stayed the plague according to the word of Moses, at the time Moses had said and at the hour appointed by Pharaoh, answering the prayer and entreaties of Moses and Aaron. The living frogs died where they were rather than disappearing instantly or returning to dust in a moment, and their bodies remained to be gathered into heaps before the Egyptians. Their dead corpses corrupted the air and polluted the atmosphere, so the effect remained even after the living plague was stayed.
Leaving the visible, corrupting heaps was deliberate, so the king and all Egypt could see them. In this way abundant evidence was given that the plague and its removal came from the God of heaven as a judgment, not from magic, which their vain philosophy could not explain away or dispose of. This differed from the rod becoming a serpent and the river turned to blood, which Pharaoh had dismissed as magic because of the magicians. Those earlier signs only hardened Pharaoh and increased his hatred of Israel. The magicians could appear to produce frogs but could not remove them.
Moses worked in this not by human influence or power but by the power of God, to convince Pharaoh that the great I AM had sent him to command Pharaoh to let Israel go that they might serve Him. Sufficient evidence was given for Pharaoh to believe if he would. Moses was chosen to break the yoke of bondage on Israel, and in that work prefigured Christ's first advent to break Satan's power over the human family and deliver those made captives by his power. Satan was on the ground and consulted with his angels to work through the magicians to counterfeit the true work of God, and the signs and wonders shown by the magicians were not by their own science alone but by the power of their god the Devil.
That counterfeiting had a two-fold purpose: to destroy the influence of what God wrought through Moses, and to reach down through all ages to destroy faith in the mighty miracles Christ would perform when He came, because Satan trembled for his power and knew his kingdom would suffer. The counterfeit work was calculated to harden Pharaoh's heart against God's power, to stagger the faith of Moses and Aaron in the divine origin of their mission, and to keep Israel from being released from Egyptian servitude to serve God. Yet God's work was shown superior to Satan's power, for the magicians could do only a few miracles and could not do all God wrought through Moses. God would not suffer Satan to proceed further, and God's controlling power cut off the channel through which Satan worked and caused even those through whom Satan wrought to feel His wrath so they could not save themselves from the plagues.
The plague polluted the Nile, which the Egyptians revered as an object of worship, and showed that their idol could not protect them from the true God's power. When Pharaoh was relieved of his immediate distress, he again stubbornly refused to let Israel go. The frogs overspreading the land in swarming multitudes and filling every place gives a picture of the way commonplace, idle, enervating, unclean, and degrading periodicals and books now overspread the land, intoxicating and ruining the mind and corrupting and destroying the soul.