Hardheartedness is a signal sin in the Bible. As Jonathan Edwards described,
Now by a hard heart is plainly meant an unaffected heart, or a heart that is not easy to be moved with virtuous affections, like a stone, insensible, stupid, unmoved, and hard to be impressed. (Religious Affections, 46)
A hard heart isn’t necessarily missing truth; gathering up more truth often makes a heart more stiff, not more soft. A hard heart is unteachable, unmovable, and often unashamed about it. Maybe worst of all, a hard heart is unaware of its condition–it has no sensitivity to its own hardness. Here is a short list of other dangers that come with hardheartedness.
First, hardheartedness prohibits love for God. There can be no warmth from a stone, no affections from a brick. Yet without love for God, there can be no relationship with Him. Hard hearts are dead cold.
Second, hardheartedness prevents teachability. There can be no interest from a calcified heart, no curiosity from old concrete. Yet without teachability, there can be no humility and no learning about Him, His requirements, or His way of salvation. Hard hearts are oblivious.
Finally, hardheartedness rejects God’s kindness and stores up wrath. The apostle Paul wrote about those who judge others but who disobey themselves. They don’t know that God’s kindness and patience and forbearance is meant to lead to repentance,
But because of your hard and impenitent (that is, without shame) heart you are storing up wrath for yourself on the day of wrath when God’s righteous judgment will be revealed. (Romans 2:5, ESV)
Though we gather to worship as Christians, as those gifted with new hearts, we diagnose some of the same sins clogging up the arteries of our hearts and threatening to smother our loves, to block our learning, to take our very lives. In order to keep our hearts from gathering plaque, we must confess our sins and seek His Spirit’s tenderizing work through the Word.