Exodus 8:18
And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man, and upon beast. And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man, and upon beast.
When Pharaoh saw relief from the frogs he hardened his heart and stubbornly refused to let Israel go. At God's command Aaron stretched out his hand, and the dust of the earth became lice throughout all Egypt. The lice came upon people and animals through God's power.
Pharaoh summoned his magicians to match the plague, and Moses and Aaron stood as servants of God acting at His command while the magicians stood as servants of Satan acting at his command. Moses wrought by the power of God and not by human influence or power to convince Pharaoh that the great I AM had sent him to free Israel. The magicians wrought not by their own science alone but by the power of their god the devil, with Satan personally on the ground directing them and coming to their aid.
The magicians tried with their enchantments to bring forth lice but could not, because the Lord would not allow them to make it appear that they could. God by His controlling power would not suffer satanic deception to proceed further and cut off the channel through which Satan worked, permitting imitation of only a few of God's miracles. Their failure proves the work of God superior to the power of Satan. The failure brought their imitative power to an end so that they could imitate Moses and Aaron no more. An earlier limit of the same kind was seen when their rods became serpents but Aaron's rod swallowed theirs.
Confronted by their inability, the magicians themselves declared to Pharaoh that the plague was the direct act of God, saying this is the finger of God. Their confession removed Pharaoh's excuse for unbelief, yet the king was still unmoved, his heart was hardened, and he did not listen. Satan worked through the magicians for a twofold purpose: to destroy the influence of what God did through Moses by counterfeiting it, and to reach down through all ages to destroy faith in the mighty miracles Christ would do at His first advent to break Satan's power and deliver captives. Moses breaking the bondage of Israel prefigured Christ coming to break Satan's power over the human family and deliver His captives.
By the same counterfeit Satan meant to harden Pharaoh against the manifestations of God's power, to stagger the faith of Moses and Aaron in the divine origin of their mission so that his instruments would prevail, and to keep Israel from being released to serve God. The plague also struck at Egyptian idolatry, because an impure insect kept worshipers from approaching the altars, thereby preventing acts of worship and exposing the powerlessness of Egypt's gods. Afterward God caused those through whom Satan had worked to feel His wrath, leaving even his own instruments unable to save themselves from the plagues that followed.