What does Judges 9:28 mean?
Gaal and his relatives have moved into Shechem, possibly returning to their home city (Judges 9:22–25). The leaders of Shechem recruited Gaal in the conflict with Abimelech, the city's appointed commander (Judges 9:1–6). After a day of partying and drinking, Gaal joins in bitter protest speeches against the king. His role is somewhat ironic because of his name. The name Ga'al bēn 'Ebed can be interpreted as "hating the son of the servant," which parallels the way Abimelech was dismissed during his coronation: as merely the child of a concubine (Judges 9:18–19).The criticism Gaal makes is that Abimelech is not a true Shechemite. He asks why the people of Shechem should serve the son of Jerubbaal, meaning Gideon (Judges 6:32). After all, Gideon never lived in Shechem. Gideon was an Israelite and an outsider. Apparently, Abimelech's officer Zebul was also an outsider of some kind. It's possible that most of the people of Shechem were non-Israelite Canaanites.
It's true that Abimelech's mother lived in Shechem (Judges 8:31). He may even have grown up in the city. For the sake of this argument, Gaal insists Abimelech's father is what really matters. The people of Shechem clearly wanted to be rid of Gideon's influence (Judges 9:2–3). In challenge, Gaal asks why any son of Gideon has the right to tell sons of Hamor—Shechem's patriarch (Judges 33:19)—what to do?