The prophet Elijah, through his dramatic demonstration of the LORD's authority and power, inspired repentance in the people of Israel, calling them to exercise His judgment on idolaters by slaying 450 prophets of Ba'al and 400 prophets of Asherah on Mount Carmel. Yet this spiritual victory was followed by a severe demonic reprisal through the woman Jezebel.
There is a fascinating true story about the Apostle John narrated by the early church "Father", Eusebius, well worth reading.
Most people have never heard of the first overseas missionary from America to Burma, Adoniram Judson. Judson was a brilliant man who learned to read when he was only 3. He went to college when he was just 16. He graduated valedictorian of his class at the age of 19. He was the son of a pastor, having been raised with Godly values, however while in college, he met a student named Jacob Eames, a deist who denied the miracles of the Bible. By the time Judson finished college he had turned completely from the Lord. For a short while, he lived a vagabond and reckless life, until a series of God-incidences turned his life inside out.
David is called a “man after God’s own heart.” Considering that he lusted after his neighbor's wife, committed adultery with her, and had her husband murdered, the Lord's description of him is remarkable. How could a man who was convicted a murderer and an adulterer also be called one after God’s own heart?