What does Judges 9:39 mean?

Zebul's plan has now come to life. When Zebul heard that Gaal had told the city's leaders that he would remove Abimelech by force if given the chance, he took the threat seriously (Judges 9:28–29). It may have been a drunken boast, but Zebul took no chances. He sent a messenger to Abimelech to ambush that city at sunrise to meet Gaal's threat head-on (Judges 9:30–34).

Gaal had no warning the attack was coming. He stood with Zebul looking to the east at sunrise only to realize several companies of soldiers were approaching from the hills. At first, Zebul stalled Gaal by telling him he was seeing things (Judges 9:35–36). Finally, Zebul taunted Gaal to back up his "big talk" by meeting Abimelech by force. Gaal does not back down. He leads the city's leaders and their fighters out to do battle with Abimelech and his forces. The very same leaders who put Abimelech in power (Judges 9:1–6) are now attempting to remove him from that position (Judges 9:22–23).