What does it mean to be 'hardened' against the truth?

The concept of hardening of heart is a serious spiritual condition often depicted in Scripture, whereby individuals resist the truth of God's Word and the call of the Gospel. As seen in Matthew 15:14, the Lord tells His disciples to leave the Pharisees; they are blind guides leading the blind. This hardening can lead to ultimate judgment as the Gospel message becomes less and less effective for the individual. It signifies a state of spiritual insensitivity and a refusal to acknowledge their sinfulness and need for a savior. This condition can lead to God's withdrawal of grace, leaving individuals vulnerable to judgment, as the vial of His wrath fills up against them.