2 Kings 10:18
And Jehu gathered all the people together, and said unto them, Ahab served Baal a little; but Jehu shall serve him much. And Jehu gathered all the people together, and said unto them, Ahab served Baal a little; but Jehu shall serve him much.
Judgment upon judgment had fallen on apostate Israel during the reign of Hazael the Syrian, who had been anointed to be the scourge and chastiser of the nation, and the stern measures of reform that included the slaying of all the house of Ahab belong to that time. Jehu's public declaration that Ahab had served Baal only a little while he himself would serve him much was not sincere, but a pretense and stratagem using religious words to disguise his purpose in order to gather all of Baal's worshipers together. Once they were assembled he had them put to death and destroyed Baal's temple, thereby bringing Baal worship in Israel to an end. That purge brought the priests of Baal and Ashtoreth to an end and threw down their altars. The same stern reform included the slaying of all the house of Ahab.
The clearing away of heathen worship was a merciful providence and provision to remove temptation, so that some in Israel might forsake heathenism, abandon it, and turn and return to God. Yet despite his religious language Jehu's heart was not right with God, which warns that close fellowship and closeness with God is needed to keep self from ruling and controlling the life and to prevent harsh, unfitting and unsuitable speech.