Judges 9:15

“ And the boxthorn said to the trees, ‘If in truth you anoint me king over you, then come and put your trust in my shadow, and if not let fire come out of the boxthorn and devour the cedars of Lebanon.' ”

The picture was deliberately ridiculous. Large trees coming and putting themselves under the shadow of the lowly boxthorn. Yet how else could he wave to and fro over the trees? Thus they would have to demean themselves and become stunted. And the boxthorn was capable of only one thing, bursting into flame and causing a forest fire.

The final phrase was Jotham's judgment. The boxthorn was good for one thing. It would burn easily. Thus it could easily be ignited in hot weather causing a forest fire, and in that fire the mightiest of the trees, the cedars of Leabanon, would be devoured. So Jotham pictured Abimelech's kingship as one that would demean them and eventually result in conflagration and destroy them all.