God hardened the Egyptian's heart because

According to the book of Exodus in the Bible, God hardened the heart of the Egyptian Pharaoh in order to gain glory over him and show his power to the people of Israel. Pharaoh had refused to let the Israelites go despite being struck by ten plagues, and God wanted to demonstrate His ultimate power and sovereignty over Pharaoh and the Egyptian gods. This ultimately led to the Israelites being freed from slavery in Egypt and their journey to the Promised Land.