The Word of God discerns the thoughts and intentions of the heart
Scripture reference
Hebrews 4:12 (ASV)
12For the word of God is living, and active, and sharper than any two-edged sword, and piercing even to the dividing of soul and spirit, of both joints and marrow, and quick to discern the thoughts and intents of the heart.
Stories
It was the Gideon's Bible, placed on a dresser, in the very room a young girl was about to commit sin that convicted her, and helped her resist the devil. For she picked the Bible, read it and asked God for forgiveness before fleeing the scene completely.
John Townsend was studying to become a clergyman when the Word of God powerfully convicted him of his own unsaved state. John abandoned his vocational ambition and sought to first know the Saviour for himself.
Two daring Christians pushed their way through to the prime minister of Romania, Gheorghiu Dej, to whom they boldly declared the Word of God. Though they were imprisoned for their daring witness, their words had sown seeds that would later bear fruit in the heart of Gheorghiu Dej.
Watchman Nee was prepared for a sermon when then Lord, using His word, began to probe Nee's life and however hard he tried, he could not escape that double-edged sword and its convicting power.