8:22. And I will make the land of Gessen wonderful in that day, so that flies shall not be there: and thou shalt know that I am the Lord in the midst of the earth.
8:23. And I will put a division between my people and thy people: to morrow shall this sign be.
8:24. And the Lord did so. And there came a very grievous swarm of flies into the houses of Pharao and of his servants, and into all the land of Egypt: and the land was corrupted by this kind of flies.
8:25. And Pharao called Moses and Aaron, and said to them: Go and sacrifice to your God in this land.
8:26. And Moses said: It cannot be so: for we shall sacrifice the abominations of the Egyptians to the Lord our God: now if we kill those things which the Egyptians worship, in their presence, they will stone us.
The abominations, etc... That is, the things they worship for Gods: oxen, rams, etc. It is the usual style of the scriptures to call all idols and false gods, abominations, to signify how much the people of God ought to detest and abhor them.
8:27. We will go three days' journey into the wilderness; and we will sacrifice to the Lord our God, as he hath commanded us.
8:28. And Pharao said: I will let you go to sacrifice to the Lord your God in the wilderness, but go no farther: pray for me.
8:29. And Moses said: I will go out from thee, and will pray to the Lord: and the flies shall depart from Pharao, and from his servants, and from his people to morrow: but do not deceive any more, in not letting the people go to sacrifice to the Lord.
8:30. So Moses went out from Pharao, and prayed to the Lord.