Albert Barnes Commentary Exodus 8:22

"And I will set apart in that day the land of Goshen, in which my people dwell, that no swarms of flies shall be there; to the end thou mayest know that I am Jehovah in the midst of the earth." — Exodus 8:22 (ASV)

I will sever ... - This severance constituted a specific difference between this and the preceding plagues. Pharaoh could not, of course, attribute the exemption of Goshen from a scourge, which fell on the valley of the Nile, to an Egyptian deity, certainly not to Chepera (see the last note), a special object of worship in Lower Egypt.