Though God’s plagues against Pharaoh continued, he hardened his heart like stone. Though his servants and wise men begged him to let Israel go, he refused. So God sent a final warning among the people, that whoever fears God should mark the doorposts of their homes with the blood of a lamb, for at midnight God would visit all who ignored His warning and take their firstborn in return for the cruelty Egypt has shown against His firstborn, Israel.