A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
jdg 9:1ABIMELECH IS MADE KING BY THE SHECHEMITES. (Jdg 9:1-6)
Abimelech the son of Jerubbaal went to Shechem--The idolatry which had been stealthily creeping into Israel during the latter years of Gideon was now openly professed; Shechem was wholly inhabited by its adherents; at least, idolaters had the ascendency. Abimelech, one of Gideon's numerous sons, was connected with that place. Ambitious of sovereign power, and having plied successfully the arts of a demagogue with his maternal relatives and friends, he acquired both the influence and money by which he raised himself to a throne.
communed . . . with all the family of the house of his mother's father--Here is a striking instance of the evils of polygamy--one son has connections and interests totally alien to those of his brothers.
jdg 9:2Whether is better for you, either that all the sons of Jerubbaal, . . . or that one reign over you--a false insinuation, artfully contrived to stir up jealousy and alarm. Gideon had rejected, with abhorrence, the proposal to make himself or any of his family king, and there is no evidence that any of his other sons coveted the title.
jdg 9:4the house of Baal-berith--either the temple, or the place where this idol was worshipped; Baal-berith, "god of the covenant," by invocation of whom the league of cities was formed.
Abimelech hired vain and light persons, which followed him--idle, worthless vagabonds, the scum of society, who had nothing to lose, but much to gain from the success of a revolutionary movement.
jdg 9:5went unto . . . Ophrah, and slew his brethren i. e., upon one stone--This is the first mention of a barbarous atrocity which has, with appalling frequency, been perpetrated in the despotic countries of the East--that of one son of the deceased monarch usurping the throne and hastening to confirm himself in the possession by the massacre of all the natural or legitimate competitors. Abimelech slew his brethren on one stone, either by dashing them from one rock, or sacrificing them on one stone altar, in revenge for the demolition of Baal's altar by their father. This latter view is the more probable, from the Shechemites (Jdg 9:24) aiding in it.
threescore and ten persons--A round number is used, but it is evident that two are wanting to complete that number.
jdg 9:6all the men of Shechem . . ., and all the house of Millo--that is, a mound or rampart, so that the meaning is, all the men in the house or temple; namely, the priests of Baal.
made Abimelech king, by the plain of the pillar--rather, "by the oak near a raised mound"--so that the ceremony of coronation might be conspicuous to a crowd.
jdg 9:7JOTHAM BY A PARABLE REPROACHES THEM. (Jdg 9:7-21)
he . . . stood in the top of mount Gerizim and lifted up his voice--The spot he chose was, like the housetops, the public place of Shechem; and the parable [Jdg 9:8-15] drawn from the rivalry of the various trees was appropriate to the diversified foliage of the valley below. Eastern people are exceedingly fond of parables and use them for conveying reproofs, which they could not give in any other way. The top of Gerizim is not so high in the rear of the town, as it is nearer to the plain. With a little exertion of voice, he could easily have been heard by the people of the city; for the hill so overhangs the valley, that a person from the side or summit would have no difficulty in speaking to listeners at the base. Modern history records a case, in which soldiers on the hill shouted to the people in the city and endeavored to instigate them to an insurrection. There is something about the elastic atmosphere of an Eastern clime which causes it to transmit sound with wonderful celerity and distinctness [HACKETT].
jdg 9:13wine, which cheereth God and man--not certainly in the same manner. God might be said to be "cheered" by it, when the sacrifices were accepted, as He is said also to be honored by oil (Jdg 9:9).
jdg 9:21Joatham . . . went to Beer--the modern village El-Bireh, on the ridge which bounds the northern prospect of Jerusalem.
jdg 9:22GAAL'S CONSPIRACY. (Jdg. 9:22-49)
When Abimelech had reigned three years--His reign did not, probably at first, extend beyond Shechem; but by stealthy and progressive encroachments he subjected some of the neighboring towns to his sway. None could "reign" in Israel, except by rebellious usurpation; and hence the reign of Abimelech is expressed in the original by a word signifying "despotism," not that which describes the mild and divinely authorized rule of the judge.
jdg 9:23Then God sent an evil spirit between Abimelech and the men of Shechem--In the course of providence, jealousy, distrust, secret disaffection, and smothered rebellion appeared among his subjects disappointed and disgusted with his tyranny; and God permitted those disorders to punish the complicated crimes of the royal fratricide and idolatrous usurper.
jdg 9:26Gaal . . . came with his brethren . . ., and the men of Shechem put their confidence in him--An insurrection of the original Canaanites, headed by this man, at last broke out in Shechem.
jdg 9:28would to God this people were under my hand--He seems to have been a boastful, impudent, and cowardly person, totally unfit to be a leader in a revolutionary crisis. The consequence was that he allowed himself to be drawn into an ambush, was defeated, the city of Shechem destroyed and strewn with salt. The people took refuge in the stronghold, which was set on fire, and all in it perished.
jdg 9:50ABIMELECH SLAIN. (Jdg 9:50-57)
Then went Abimelech to Thebez, and encamped against Thebez--now Tubas--not far from Shechem.
jdg 9:51all the men and women, . . . gat them up to the top of the tower--The Canaanite forts were generally mountain fastnesses or keeps, and they often had a strong tower which served as a last refuge. The Assyrian bas-reliefs afford counterparts of the scene here described so vivid and exact, that we might almost suppose them to be representations of the same historic events. The besieged city--the strong tower within--the men and women crowding its battlements--the fire applied to the doors, and even the huge fragments of stone dropping from the hands of one of the garrison on the heads of the assailants, are all well represented to the life--just as they are here described in the narrative of inspired truth [GOSS].