if you then have dealt truly and righteously with Jerubbaal and with his house this day, then rejoice you in Abimelech, and let him also rejoice in you:
In other words, he's an outsider. We ought to be serving Hamor and his family, let them be the kings. And he said to God the people were under my rule, because I can really do a good job here, you know. Who's Abimelech? And so he said if you would just commit yourself to me I would remove Abimelech.