With the fourth plague, God introduces a distinction that will repeat for the remaining plagues: that day in the land of Goshen where My people dwell, there no swarms of wild beasts shall be (Exodus 8:18). Targum Pseudo-Jonathan on Exodus 8:18 preserves the punchline: that thou mayest know that I the Lord am the Ruler in the midst of the land.
This is the theological center of the plagues. Up until now, Pharaoh might have argued that the disasters were bad weather, sympathetic magic, or cosmic imbalance. But the moment Goshen is spared, all those arguments collapse. A random catastrophe does not draw property lines. A targeted judgment does.
The Aramaic word the meturgeman uses for God — shallit, Ruler — is a political term. Pharaoh claims to be shallit. Now the real shallit is demonstrating jurisdiction. He draws a line around Goshen. The wild beasts obey the line. The animals of the desert know a border that the king of Egypt does not.
And listen to the phrase: in the midst of the land. Not in the sky. Not far away. The God of Israel is not a distant deity who throws plagues from orbit. He is ruling inside Egypt — in its streets, on its property lines, at its animals' behavior. Pharaoh's sovereignty has been quietly replaced inside his own country.
The takeaway: there is no corner of any empire that is not already God's. The plagues announce what the Psalms would later say — the earth is the Lord's, and the fullness thereof (Psalm 24:1).