What does Judges 9:7-20 mean?

When it was told to Jotham, he went and stood on top of Mount Gerizim and cried aloud and said to them, “Listen to me, you leaders of Shechem, that God may listen to you. The trees once went out to anoint a king over them, and they said to the olive tree, ‘Reign over us.’ But the olive tree said to them, ‘Shall I leave my abundance, by which gods and men are honored, and go hold sway over the trees?’ And the trees said to the fig tree, ‘You come and reign over us.’ But the fig tree said to them, ‘Shall I leave my sweetness and my good fruit and go hold sway over the trees?’ And the trees said to the vine, ‘You come and reign over us.’ But the vine said to them, ‘Shall I leave my wine that cheers God and men and go hold sway over the trees?’ Then all the trees said to the bramble, ‘You come and reign over us.’ And the bramble said to the trees, ‘If in good faith you are anointing me king over you, then come and take refuge in my shade, but if not, let fire come out of the bramble and devour the cedars of Lebanon.’ “Now therefore, if you acted in good faith and integrity when you made Abimelech king, and if you have dealt well with Jerubbaal and his house and have done to him as his deeds deserved— for my father fought for you and risked his life and delivered you from the hand of Midian, and you have risen up against my father’s house this day and have killed his sons, seventy men on one stone, and have made Abimelech, the son of his female servant, king over the leaders of Shechem, because he is your relative— if you then have acted in good faith and integrity with Jerubbaal and with his house this day, then rejoice in Abimelech, and let him also rejoice in you. But if not, let fire come out from Abimelech and devour the leaders of Shechem and Beth-millo; and let fire come out from the leaders of Shechem and from Beth-millo and devour Abimelech.”

English Standard Version (ESV)