“And afterward Moses and Aaron went in, and told Pharaoh, Thus saith the LORD God of Israel, Let my people go, that they may hold a feast unto me in the wilderness.”
King James Version (KJV)
5:1 Thus saith the Lord God of Israel, Let my people go - Moses, in treating with the elders of Israel, is directed to call God the God of their fathers; but, in treating with Pharaoh, they call him the God of Israel, and it is the first time we find him called so in scripture. He is called the God of Israel, the person, #Gen 33:20|, but here it is Israel the people. They are just beginning to be formed into a people when God is called their God. Let my people go - They were God's people, and therefore Pharaoh ought not to detain them in bondage. And he expected services and sacrifices from them, and therefore they must have leave to go where they could freely exercise their religion, without giving offence to, or receiving offence from, the Egyptians.