Exodus 9:29 - Ellicott's Commentary On The Whole Bible

That thou mayest know how that the earth is the Lord’s. — Comp, Exodus 9:15. It was the general belief of the Egyptians, as of most ancient nations, that each country had its own god or gods. Pharaoh had already admitted Jehovah’s power (Exodus 8:8), and now regarded Him as the God of the Hebrews (Exodus 8:28). God desired to have it generally acknowledged that He was the God of the whole earth.