“ Then all the trees said to the boxthorn, ‘You come and reign over us.' ”
Now the trees were getting desperate. They are pictured as foolishly longing for a king over them, come what may. They went to the lowest tree of all, the boxthorn which could not be used for timber, bore no edible fruit and hurt men with its thorns. It was renowned for its thorniness (Psalms 58:9).
So Jotham pictures Abimelech as a boxthorn, useless and prickly, who was only offered the position because no one better would take it, for none other wanted full kingship.