Why should you harden your hearts just as the Egyptians and Pharaoh hardened their hearts? Isn't it true that after God toyed with them, they let Israel go, and off they went?

Then Samuel told the whole house of Israel, "If you're returning to the LORD with all your heart, then remove the foreign gods and the Ashtaroth from among you, direct your hearts back to the LORD, and serve him only. Then he will deliver you from the control of the Philistines."