What does Judges 9:5 mean?

In a terrible scene, Abimelech (Judges 8:30–31) goes to the home of his father Gideon in the town of Ophrah. To become undisputed heir to Gideon's authority, Abimelech must eliminate his brothers. He approaches with a gang of hired goons (Judges 9:1–4). With the help of these "worthless and reckless" men, depicted as brutish hooligans, he kills all but one of the seventy sons of Gideon (Judges 8:30).

While the text doesn't mention it, it's easy to imagine Abimelech carried resentment toward his father and his brothers. He was the son of a concubine, not a "full" wife. He likely had no hope of enjoying the status of other sons of a renowned man. To dishonor his father with open brutality, so soon after his death, suggests deep anger toward that side of his family. Gideon's choice to take the Shechemite woman—almost certainly a Canaanite (Deuteronomy 7:3–4)—as his concubine brings destruction to his entire family.

Murdering nearly seventy people is bad enough. Worse, the text says these killings took place "on one stone." This means the brothers were not merely assassinated but rounded up and publicly executed—possibly even in a ritual style. Some commentators speculate the murders were carried out on an altar dedicated to Baal-berith (Judges 8:33), though this would have been unusual. It's also possible Abimelech killed the male children of those sons, as well, to remove their claims to leadership.

Only the youngest brother escapes the carnage, hiding from Abimelech's men. His name is Jotham, but no other details are given. He will live to cast a prophetic shadow over Abimelech's coronation by the people of Shechem (Judges 9:7).