We could never understand the awful events in these verses unless we remember two things, (1) that a perfect and holy God has put them in the Bible, and (2) that He sooner or later punishes every sin that is ever committed. Either you will be cast into hell for your sins, or Jesus has been punished for every one of your sins.
V.1 Samaria was the capital, Jezreel was a place in Israel; Jerusalem was the capital of the kingdom of Judah.
V.2-3 King Jehu uses these strange methods to do what God had told him to do.
V.4-5 The leaders of Israel are afraid, for they suspect something is going wrong.
V.6-7 The severe punishment from God falls on these seventy princes, the sons of wicked king Ahab.
V.9-11 Not only the princes, but all these four groups. It was total removal from the earth of all those who had served Ahab. Remember this is a picture of God’s righteous punishment of every unrepentant sinner today.
V.12-17 These men, who had come from the King of Judah, were killed on orders from Jehu, he even boasts of his zeal for the Lord in all that he was doing!