In the morning, just when he sets out for the water, go to Pharaoh and present yourself by the bank of the Nile, holding in your hand the staff that turned into a snake.
and the magicians said to Pharaoh, “This is the finger of God.” Yet Pharaoh hardened his heart and would not listen to them, just as the Lord had said. Fourth Plague: The Flies.
But although Pharaoh found upon inquiry that not even so much as one of the livestock of the Israelites had died, he remained obstinate and would not let the people go. Sixth Plague: The Boils.
And they made their hearts as hard as diamond so as not to hear the instruction and the words that the Lord of hosts had sent by his spirit through the earlier prophets. So great anger came from the Lord of hosts:
But Sihon, king of Heshbon, refused to let us pass through his land, because the Lord, your God, made him stubborn in mind and obstinate in heart that he might deliver him into your power, as indeed he has now done.
See that you do not reject the one who speaks. For if they did not escape when they refused the one who warned them on earth, how much more in our case if we turn away from the one who warns from heaven.
Why should you become stubborn, the way the Egyptians and Pharaoh were stubborn? Was it not after he had dealt ruthlessly with them that the Israelites were released and departed?