Why is unbelief considered a sin?

Unbelief is often referred to as the root of many spiritual struggles. In Hebrews 3:12, unbelief is called an 'evil heart' that departs from the living God. This rejection of faith not only impacts one’s relationship with God but also hinders spiritual growth and the experience of God's promises. When individuals fail to trust in God's word and His character, they ignore the evidence of His faithfulness displayed throughout Scripture. Belief in God and His promises is essential for entering into true rest and salvation, and unbelief limits that communion, leading to spiritual stagnation and despair.