Hardness of heart is a phrase that uses the idea of something hard that cannot be changed, like stone. It describes someone who stubbornly refuses to listen to God or change their ways.
The Story of Pharaoh's Hard Heart
The Bible first talks about hardness of heart in the story of Pharaoh, ruler of Egypt in the time of Moses. This is an important example that helps us understand what hardness of heart means. The Bible mentions Pharaoh's hardened heart at least 20 times in the Old Testament. Later, Paul writes about what this means in Romans 9:17–24.
The first mention is in Exodus 4:21, where God promises Moses that he will harden Pharaoh’s heart so he will not allow the Israelites to leave. This promise is repeated in Exodus 7:3, 14:4, and 17, and happens in 7:13–14. God performed many miracles that Pharaoh saw with his own eyes. God also warned Pharaoh about what would happen if he did not obey. When Pharaoh refused to listen, God sent ten terrible plagues to Egypt.
The Bible makes clear that Pharaoh’s stubbornness was part of God’s plan for his own ends and purposes (Exodus 9:16; Joshua 11:20; compare Romans 9:17–18). But it also says that Pharaoh hardened his own heart (Exodus 8:15, 32; 9:34; 13:15). This shows that hardening the heart is a result of rejecting the truth. This is an important point in the Bible. Hardening of the heart is not only something God allows to happen to a person but also a choice to turn away from the truth. Because of this, the person is responsible to God for their hard heart.
How Hearts Become Hard
Paul explains in Romans 1:18–32 how people's hearts become hard. Everyone naturally knows something about God, but they choose to reject this knowledge. They take what is true about God and turn it into lies. They try to hide the truth they know.
Because of this, their hearts become hard. Paul says their hearts become "darkened" when God lets them follow their sinful ways. This leads to intellectual, moral, and social consequences. Paul calls this a “hard and unrepentant heart” in Romans 2:5. He explains that these people are not just fighting against God's punishment or the results of their sins. Instead, they are fighting against the truth and against what they know in their hearts is right (Romans 2:14–16).
Warnings About Hard Hearts
Many times in the Bible, God warns people not to let their hearts become hard. A hard heart shows that someone does not believe in God (Deuteronomy 15:7; Hebrews 3:8, 15; 4:7). Jesus felt deep sadness when he saw people's hard hearts (Mark 3:5; 16:14). In one example, Jesus explained that Moses allowed divorce only because people's hearts were too hard to follow God's original plan for marriage (Matthew 19:8).
The Gospels tell us that sometimes God makes people unable to understand spiritual truth (Matthew 13:13–15; John 12:39–41). When people keep refusing to obey God, their hearts become harder and harder. This shows their deeper rebellion against God (Psalm 95:8; John 12:40; Hebrews 3:8, 15; 4:7). The Bible shows many examples of this when God's people turned away from following him (2 Kings 17:14; Nehemiah 9:16–17; Hebrews 3:8).