1. Jehu purges Ahab's line (1-17)

Out of fear of Jehu, the 70 sons of Ahab were assassinated. Any relative of Ahab, including relatives of Ahaziah king of Judah, who was also a relative of Ahab, were killed. This fulfilled the word of the LORD spoken to Elijah (10,17). Jehu had zeal for the LORD.

2. Jehu purges Israel's Baal worship (18-36)

Jehu held a mock Baal worship service in order to destroy all the servants and priests of Baal. So Jehu destroyed Baal worship in Israel, but he didn't destroy the golden calves (28-29). Jehu did well to carry out the LORD's purges of Ahab's line and Baal worship. But he did not keep God's law with all his heart (31), by clinging to some sins of idolatry.