Charles Ellicott 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 in that day the land of Goshen.—This was a new feature, and one calculated to make a deep impression both on king and people. The “land of Goshen” can only have been some portion of the Eastern Delta, a tract in no way different from the rest of Egypt—low, flat, well-watered, fertile. Nature had put no severance between it and the regions where the Egyptians lived; so the severance to be made would be a manifest miracle.