Moses asks Pharaoh to let the Hebrews go to sacrifice to God, but Pharaoh instead makes their work harder, as slaves are not to petition Pharaoh. The overseers see that the workload is too much but Pharaoh calls the workers idle, as they are asking for time to spend worshipping God.
When Pharaoh refuses, God hardens Pharaoh's heart initially to show His great power, but soon Pharaoh hardens his own heart. God provides the sign of a rod that turns into a snake, similar to a trick that the Egyptian magicians would do, but God's miracle proves that it is no trick. When Pharaoh is not moved, God turns the river red, and then sends a plague of frogs and then gnats. Even the magicians are convinced that this is not a trick at this point, but Pharaoh is unmoved. After a plague of flies, Pharaoh offers to allow the Hebrews to worship in Egypt, but Moses knows that this will merely anger the Egyptians. Pharaoh then allows Moses to sacrifice outside of Egypt, but would not let the Hebrews go.