What does Judges 9:28 mean?

Gaal, son of Ebed, said, 'Who is Abimelech, and why should we serve him? Isn’t he just Jerubbaal’s son, and isn’t Zebul his officer? Serve the people of Hamor, Shechem’s founder! Why should we serve Abimelech?' Judges 9:28 - Modern Text Bible

(Gaal questions Abimelech’s right to rule, stirring up the people by appealing to their local heritage.)