Exodus 10:3
And Moses and Aaron came in unto Pharaoh, and said unto him, Thus saith the LORD God of the Hebrews, How long wilt thou refuse to humble thyself before me? let my people go, that they may serve me. And Moses and Aaron came in unto Pharaoh, and said unto him, Thus saith the LORD God of the Hebrews, How long wilt thou refuse to humble thyself before me? let my people go, that they may serve me.
Moses and Aaron came again into Pharaoh's presence bearing the LORD God of the Hebrews' question of how long he would refuse to humble himself before Him, with the command to let His people go that they might serve Him. That demand was pressed amid the plagues that laid bare the powerlessness of Egypt's idols and asserted Jehovah's supremacy and His authority to deliver His people. In this confrontation Pharaoh was given a choice to humble himself and release Israel or to refuse and suffer the plague of locusts. Refusal would bring locusts to cover the face of the earth and devour the residue that had escaped the hail. He resisted the command and would not let the families go.
God had long borne with Pharaoh's continual rebellion and suffered him to go on resisting in order to show His great signs and wonders before Pharaoh and Israel. Those signs were to confirm Israel's faith in Him as the only true and living God and to give unmistakable evidence of the distinction He placed between the Egyptians and His people. They were to enable Israel to tell their sons and grandsons what He had wrought in Egypt, that they might know that He is the LORD. They were also to make known to all nations that He had chosen Israel as His peculiar people despite their hard labor and contempt, and that He would work wonderfully for their deliverance.