Definition and Nature:
Hardness of heart refers to a spiritual condition characterized by an insensitivity or resistance to God's voice, commands, and presence. It is a state where an individual becomes obstinate, unyielding, and closed off to divine influence and moral conviction. This condition is often depicted in Scripture as a grave spiritual ailment that can lead to severe consequences.

Biblical Instances:
The Bible provides numerous examples of individuals and groups who exhibited hardness of heart. One of the most notable examples is Pharaoh during the Exodus narrative. Despite witnessing numerous signs and wonders performed by God through Moses, Pharaoh repeatedly hardened his heart, refusing to let the Israelites go (Exodus 7:13: "Yet Pharaoh’s heart was hardened, and he would not listen to them, just as the LORD had said").

The Israelites themselves also displayed hardness of heart during their wilderness journey. Despite God's continuous provision and guidance, they frequently rebelled and doubted His promises. Psalm 95:8-9 warns, "Do not harden your hearts as you did at Meribah, as you did that day at Massah in the wilderness, where your fathers tested and tried Me, though they had seen My work."

In the New Testament, Jesus encounters hardness of heart among the Pharisees and religious leaders who resisted His teachings and miracles. Mark 3:5 describes Jesus' reaction: "And He looked around at them with anger, grieved by their hardness of heart."

Causes:
Several factors contribute to the development of a hardened heart. Persistent sin and disobedience can desensitize an individual to God's voice. Hebrews 3:13 warns, "But exhort one another daily, as long as it is called today, so that none of you may be hardened by sin’s deceitfulness."

Pride and self-reliance also play significant roles. When individuals trust in their own understanding and abilities rather than seeking God's wisdom, they risk hardening their hearts. Proverbs 28:14 states, "Blessed is the man who is always reverent, but he who hardens his heart falls into trouble."

Consequences:
The consequences of a hardened heart are severe and far-reaching. Spiritually, it leads to a separation from God and an inability to perceive His truth and love. Romans 1:21 illustrates this, "For although they knew God, they neither glorified Him as God nor gave thanks to Him, but they became futile in their thinking and darkened in their foolish hearts."

A hardened heart can also result in judgment and discipline from God. In the case of Pharaoh, his persistent hardness led to the plagues and ultimately the destruction of Egypt's firstborn (Exodus 11:10: "Moses and Aaron performed all these wonders before Pharaoh, but the LORD hardened Pharaoh’s heart so that he would not let the Israelites go out of his land").

Prevention and Remedy:
To prevent and remedy hardness of heart, Scripture encourages believers to remain humble, obedient, and receptive to God's Word. Regular self-examination and repentance are vital. Psalm 139:23-24 is a prayer for divine examination: "Search me, O God, and know my heart; test me and know my concerns. See if there is any offensive way in me; lead me in the way everlasting."

Engaging in community and mutual encouragement is also essential. Hebrews 10:24-25 advises, "And let us consider how to spur one another on to love and good deeds. Let us not neglect meeting together, as some have made a habit, but let us encourage one another, and all the more as you see the Day approaching."

Ultimately, a softened heart is one that is responsive to the Holy Spirit, open to correction, and eager to follow God's will.