His half-brothers were motivated by greed for their inheritance as well as disdain for his status as a bastard son and thus not a full citizen of Israel (Deuteronomy 23:2). And so they forced him out of his father’s home against his will.
But there was no law that allowed for a bastard to be driven from the house and given nothing whatsoever. The action of Jephthah’s brothers was thus cruel and wicked. With this act they betray their half-brother and in so doing violate Israelite laws enjoining care and compassion for the outcast (e.g., Deuteronomy 10:12–22).
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2 And Gilead’s wife also bore him sons. And when his wife’s sons grew up, they drove Jephthah out and said to him, “You shall not have an inheritance in our father’s house, for you are the son of another woman.”