Then the Lord said unto Moses, Go in unto Pharaoh and tell him, Thus saith the Lord God of the Hebrews, Let My people go that they may serve Me. This was now the standing formula of demand.
Related Commentaries of Exodus 9:1
Exodus 9:1
1 Then the LORD said unto Moses, Go in unto Pharaoh, and tell him, Thus saith the LORD God of the Hebrews, Let my people go, that they may serve me.