Judges 9:16-18

“Now therefore, if you have dealt truly and uprightly, in that you have made Abimelech king, if you have dealt well with Jerubbaal, and his house, and have done to him according to the deserving of his hands, for my father fought for you and ventured his life (‘cast his life before him') and delivered you out of the hand of Midian, but you are risen up against my father's house this day, and have slain his sons, all seventy, on one stone, and have made Abimelech, the son of his bondwoman, king over the men of Shechem, because he is your brother;”

Jotham now outlined the position that they had taken and challenged them to justify it. They were of those who had requested that Gideon, and his sons after him, might reign over them. And they had not meant the ‘son of a bondwoman' (Jotham's aristocratic scorn is palpable). They had meant his full sons who had the right to inherit. Let them now consider whether they were dealing fairly and uprightly. Were they even doing what they themselves had requested? They did it originally because they knew such sons would be worthy, because they would be sons like Gideon. And yet now they were accepting, not an olive tree or a fig tree or a vine, all of which had been on offer to them, but a boxthorn.

Furthermore let them consider that Gideon hazarded his life for their sakes, and delivered them from a most terrible situation, for Shechem had suffered from the Midianite incursions along with the rest. And what reward were they now giving him? Have they done what their hero deserved, in rising up and destroying his full sons, and doing it in the most heinous way? And then finishing up by giving his inheritance to one who had no right to it? And they were doing it for purely selfish reasons. There was no honour in it, no high feelings. They were doing it for what they could get out of it. They were doing it simply because Abimelech was related to them, and they thought they could control him.

Note the constant use of seventy. It was not the exact number that mattered, (if the seventy had been originally exact then only sixty nine had been slain) it was what the number signified, it signified those who were within the sphere of the divine perfection. Their sin was thus against Yahweh.