Then the Lord told Moses, "I have one more disaster to bring against Pharaoh and Egypt. After this, he will ask you to leave Egypt. In fact, he will force you to leave this country.
and every firstborn son in Egypt will die, from the firstborn son of Pharaoh, the ruler of Egypt, to the firstborn son of the slave girl grinding grain. Even the firstborn animals will die.
But none of the Israelites or their animals will be hurt— not even a dog will bark at them.' Then you will know that the Lord has treated Israel differently from Egypt.
All these officials of yours will come down and bow to me. They will say, 'Leave and take all your people with you.' Only then will I leave!" Then in anger, Moses left the meeting with Pharaoh.
That is why Moses and Aaron did all these great miracles in front of Pharaoh. And that is why the Lord made Pharaoh so stubborn that he would not let the Israelites leave his country.