The bramble - Said to be the Rhamnus Paliurus of Linnaeus, otherwise called Spina-Christi, or Christ's Thorn, a shrub with sharp thorns. The application is obvious. The noble Gideon and his worthy sons had declined the proffered kingdom. The vile, base-born Abimelech had accepted it, and his act would turn out to the mutual ruin of himself and his subjects.

Then said all the trees unto the bramble - The word אטד atad, which we translate bramble, is supposed to mean the rhamnus, which is the largest of thorns, producing dreadful spikes, similar to darts. See Theodoret on Psalm 58:10. There is much of the moral of this fable contained in the different kinds of trees mentioned.
1. The olive; the most profitable tree to its owner, having few equals either for food or medicine.
2. The fig tree; one of the most fruitful of trees, and yielding one of the most delicious fruits, and superior to all others for sweetness.
3. The vine, which alone yields a liquor that, when properly prepared, and taken in strict moderation, is friendly both to the body and mind of man, having a most direct tendency to invigorate both.
4. The bramble or thorn, which, however useful as a hedge, is dangerous to come near; and is here the emblem of an impious, cruel, and oppressive king.
As the olive, fig, and vine, are said in this fable to refuse the royalty, because in consequence, they intimate, they should lose their own privileges, we learn that to be invested with power for the public good can be no privilege to the sovereign. If he discharge the office faithfully, it will plant his pillow with thorns, fill his soul with anxious cares, rob him of rest and quiet, and, in a word, will be to him a source of distress and misery. All this is represented here under the emblem of the trees losing their fatness, their sweetness and good fruits, and their cheering influence. In short, we see from this most sensible fable that the beneficent, benevolent, and highly illuminated mind, is ever averse from the love of power; and that those who do seek it are the thoughtless, the vain, the ambitious, and those who wish for power merely for the purpose of self-gratification; persons who have neither the disposition nor the knowledge to use power for the advantage of the community; and who, while they boast great things, and make great pretensions and promises, are the tyrants of the people, and often through their ambition, like the bramble in the fable kindle a flame of foreign or domestic war, in which their subjects are consumed. The sleepless nights and corroding cares of sovereignty, are most forcibly described by a poet of our own, whose equal in describing the inward workings of the human heart, in all varieties of character and circumstances, has never appeared either in ancient or modern times. Hear what he puts in the mouth of two of his care-worn kings: -
"How many thousand of my poorest subjects
Are at this hour asleep? - Sleep, gentle sleep,
Nature's soft nurse! how have I frighted thee,
That thou no more wilt weigh my eyelids down,
And steep my senses in forgetfulness?
Why rather, sleep, liest thou in smoky cribs,
Upon uneasy pallets stretching thee,
And hush'd with buzzing night-flies to thy slumber
Than in the perfumed chambers of the great,
Under the canopies of costly state,
And lull'd with sounds of sweetest melody?
O thou dull god! why liest thou with the vile
In loathsome beds; and leav'st the kingly couch
A watch-case, or a common 'larum bell?
Wilt thou upon the high and giddy mast
Seal up the ship-boy's eyes, and rock his brains
In cradle of the rude imperious surge;
And in the visitation of the winds,
Who take the ruffian billows by the top,
Curling their monstrous heads and hanging them,
With deafening clamours, in the slippery clouds,
That, with the hurly, death itself awakes?
Canst thou, O partial sleep! give thy repose
To the wet sea-boy, in an hour so rude;
And, in the calmest and most stillest night,
With all appliances and means to boot,
Deny it to a king? Then, happy low, lie down!
Uneasy lies the head that wears a crown." -
"O hard condition! twin-born with greatness,
Subjected to the breath of every fool,
Whose sense no more can feel but his own wringing!
What infinite heart's ease must kings neglect,
That private men enjoy!
And what have kings, that privates have not too,
Save ceremony, save general ceremony?" -
"'Tis not the balm, the scepter, and the ball,
The sword, the mace, the crown imperial,
The intertissued robe of gold and pearl,
The farced title running 'fore the king,
The throne he sits on, nor the tide of pomp
That beats upon the high shore of this world,
No, not all these, thrice gorgeous ceremony,
Not all these, laid in bed majestical,
Can sleep so soundly as the wretched slave."
Shakespeare
This is precisely the sentiment expressed in the denial of the olive, fig tree, and vine.

Then said all the trees unto the bramble,.... Perceiving they could not prevail upon any of the useful and fruitful trees to take the government of them, they unite in a request to a bramble, scarce to be called a tree, and however a very barren and fruitless one, yea, hurtful and distressing:
come thou, and reign over us; this respects Abimelech, and describes him as a mean person, the son of a concubine, as having no goodness in him, not any good qualifications to recommend him to government, but all the reverse, cruel, tyrannical, and oppressive; and this exposes the folly of the Shechemites, and their eagerness to have a king at any rate, though ever so mean and despicable, useless and pernicious.

Bramble - Or, thorn, fitly representing Abimelech, the son of a concubine, and a person of small use, and great cruelty.