1 And afterward Moses and Aaron came and said to Pharaoh, “Thus says the LORD, the God of Israel, `Let My people go that they may celebrate a feast to Me in the wilderness.'” 2 But Pharaoh said, “Who is the LORD that I should obey His voice to let Israel go? I do not know the LORD, and besides, I will not let Israel go.” 3 Then they said, “The God of the Hebrews has met with us. Please, let us go a three days’ journey into the wilderness that we may sacrifice to the LORD our God, otherwise He will fall upon us with pestilence or with the sword.” 4 But the king of Egypt said to them, “Moses and Aaron, why do you draw the people away from their work? Get back to your labors!” 5 Again Pharaoh said, “Look, the people of the land are now many, and you would have them cease from their labors!” 6 So the same day Pharaoh commanded the taskmasters over the people and their foremen, saying, 7 “You are no longer to give the people straw to make brick as previously; let them go and gather straw for themselves. 8 “But the quota of bricks which they were making previously, you shall impose on them; you are not to reduce any of it. Because they are lazy, therefore they cry out, `Let us go and sacrifice to our God.’ 9 “Let the labor be heavier on the men, and let them work at it so that they will pay no attention to false words.”
10 So the taskmasters of the people and their foremen went out and spoke to the people, saying, “Thus says Pharaoh, `I am not going to give you any straw. 11 `You go and get straw for yourselves wherever you can find it,but none of your labor will be reduced.'” 12 So the people scattered through all the land of Egypt to gather stubble for straw. 13 The taskmasters pressed them, saying, “Complete your work quota, your daily amount, just as when you had straw.” 14 Moreover, the foremen of the sons of Israel, whom Pharaoh’s taskmasters had set over them, were beaten and were asked, “Why have you not completed your required amount either yesterday or today in making brick as previously?”
There is a key phrase in here. Pharaoh said, ‘I do not know the Lord…” Of course He didn’t, but God was going to reveal Himself to Pharaoh, and then He would know why He should let the people go. Until someone knows who God is, they can’t grasp much of what you say when you speak of Him. But let God speak through you, and they’ll find out in short order.