What does 2 Kings 9:18 mean?

but king Joram had returned to be healed in Jezreel of the wounds which the Syrians had given him, when he fought with Hazael king of Syria.) Jehu said, “If this is your thinking, then let no one escape and go out of the city, to go to tell it in Jezreel.”

So Jehu rode in a chariot and went to Jezreel, for Joram lay there. Ahaziah king of Judah had come down to see Joram.

Now the watchman was standing on the tower in Jezreel, and he spied the company of Jehu as he came, and said, “I see a company.” Joram said, “Take a horseman, and send to meet them, and let him say, ‘Is it peace?’”

Then he sent out a second on horseback, who came to them, and said, “Thus says the king, ‘Is it peace?’” Jehu answered, “What do you have to do with peace? Fall in behind me!”

The watchman said, “He came to them, and isn’t coming back. The driving is like the driving of Jehu the son of Nimshi, for he drives furiously.”

Joram said, “Get ready!” They got his chariot ready. Then Joram king of Israel and Ahaziah king of Judah went out, each in his chariot, and they went out to meet Jehu, and found him on Naboth the Jezreelite’s land.