21 Else, if you will not let my people go, behold, I will send swarms of flies on you and your servants and your people, and into your houses; and the houses of the Egyptians shall be filled with swarms of flies, and also the ground on which they stand. 22 But on that day I will set apart the land of Goshen, where my people dwell, so that no swarms of flies shall be there; that you may know that I am the Lord in the midst of the earth. 23 Thus I will put a division between my people and your people. By tomorrow shall this sign be."'" 24 And the Lord did so; there came great swarms of flies into the house of Pharaoh and into his servants' houses, and in all the land of Egypt the land was ruined by reason of the flies. 25 Then Pharaoh called Moses and Aaron, and said, "Go, sacrifice to your God within the land." 26 But Moses said, "It would not be right to do so; for we shall sacrifice to the Lord our God offerings abominable to the Egyptians. If we sacrifice offerings abominable to the Egyptians before their eyes, will they not stone us? 27 We must go three days' journey into the wilderness and sacrifice to the Lord our God as he will command us." 28 So Pharaoh said, "I will let you go, to sacrifice to the Lord your God in the wilderness; only you shall not go very far away. Make entreaty for me." 29 Then Moses said, "Behold, I am going out from you and I will pray to the Lord that the swarms of flies may depart from Pharaoh, from his servants, and from his people, tomorrow; only let not Pharaoh deal falsely again by not letting the people go to sacrifice to the Lord." 30 So Moses went out from Pharaoh and prayed to the Lord. 31 And the Lord did as Moses asked, and removed the swarms of flies from Pharaoh, from his servants, and from his people; not one remained.
Matthew Henry's Commentary on Exodus 8:21-31
Commentary on Exodus 8:20-32
(Read Exodus 8:20-32)
Pharaoh was early at his false devotions to the river; and shall we be for more sleep and more slumber, when any service to the Lord is to be done? The Egyptians and the Hebrews were to be marked in the plague of flies. The Lord knows them that are his, and will make it appear, perhaps in this world, certainly in the other, that he has set them apart for himself. Pharaoh unwillingly entered into a treaty with Moses and Aaron. He is content they should sacrifice to their God, provided they would do it in the land of Egypt. But it would be an abomination to God, should they offer the Egyptian sacrifices; and it would be an abomination to the Egyptians, should they offer to God the objects of the worship of the Egyptians, namely, their calves or oxen. Those who would offer acceptable sacrifice to God, must separate themselves from the wicked and profane. They must also retire from the world. Israel cannot keep the feast of the Lord, either among the brick-kilns or among the flesh-pots of Egypt. And they must sacrifice as God shall command, not otherwise. Though they were in slavery to Pharaoh, yet they must obey God's commands. Pharaoh consents for them to go into the wilderness, provided they do not go so far but that he might fetch them back again. Thus, some sinners, in a pang of conviction, part with their sins, yet are loth they should go very far away; for when the fright is over, they will turn to them again. Moses promised the removal of this plague. But let not Pharaoh deal deceitfully any more. Be not deceived; God is not mocked: if we think to cheat God by a sham repentance and a false surrender of ourselves to him, we shall put a fatal cheat upon our own souls. Pharaoh returned to his hardness. Reigning lusts break through the strongest bonds, and make men presume and go from their word. Many seem in earnest, but there is some reserve, some beloved, secret sin. They are unwilling to look upon themselves as in danger of everlasting misery. They will refrain from other sins; they do much, give much, and even punish themselves much. They will leave it off sometimes, and, as it were, let their sin depart a little way; but will not make up their minds to part with all and follow Christ, bearing the cross. Rather than that, they venture all. They are sorrowful, but depart from Christ, determined to keep the world at present, and they hope for some future season, when salvation may be had without such costly sacrifices; but, at length, the poor sinner is driven away in his wickedness, and left without hope to lament his folly.