Either,
1. Of the whole earth, and consequently of Egypt, that I am not only the Lord of Israel, but of thee and thy dominions too. God is here spoken of after the manner of earthly princes, who use to reside in the midst of their kingdoms, that they may more conveniently rule and influence them. Or rather,
2. Of Goshen; the words being properly thus rendered, that I the Lord am in the midst of that land, to wit, the land of Goshen now spoken of, to defend and preserve it. For God is said to be in the midst of them whom he protects, Deuteronomy 7:21, Deuteronomy 23:14 Joshua 3:10 Psalms 46:5; and not to be in the midst of others whom he forsakes, and designs or threatens to destroy, Numbers 14:42 Deuteronomy 1:42, Deuteronomy 31:17. Compare Exodus 33:3, with Exodus 34:9.