Verses 1-6: Abimelech conspires to become king by way of reasoning that he is flesh and blood to Jerubbaal’s brothers. And these brothers also work for Abimelech, to help convince the men that Abimelech should be king. Abimelech takes their agreement as some sort of twisted permission to go ahead and kill his seventy brothers, all upon the same stone. Only one brother named Jotham escapes. Abimelech is made king by the terebinth tree.
Verses 7-21: In these verses, Jotham is calling the men on their bluff, the men that choose Abimelech to be their king. Jotham describes to them through a parable of trees that Abimelech is not suited to be king. Indeed, there were other men that were more suited to be king, but they resisted the offer so that they might be able to continue serving God and their fellow citizens. These other men are represented as beneficial trees, and humble, while Abimelech is represented as a threatening bramble.
Jotham reminds the men how Gideon brought them out from under the Midianites, and that Abimelech was the son of one of Gideon’s female servants. Through Jotham’s speech to them, it would seem that Jotham thinks that the men should know better than to trust an ungodly man like Abimelech as their king. Jotham concludes in this part of the chapter by encouraging conflict between the men of Shechem and Abimelech. Then Jotham flees to Beer to hide from Abimelech.
There is an overall impression that the men in Israel continue to lack complete faith in God even by now. Why else would they go to such an evil man like Abimelech for their leader?
Jotham’s example is certainly a strong one, and he is the only one mentioned that saw through the facade of Abimelech’s “leadership.”
Also, did they even need a king? No. They needed God, and they did not seek Him. They needed Him the most and instead sought after a corrupt leader, supporting Abimelech with money from an idol’s treasury. We should be careful how much trust we put in men, their words and their actions. They are a far cry from the perfect leadership of the Lord and the purity of His message. You really can’t beat the real thing.