John Gill Commentary Judges 9:56

"Thus God requited the wickedness of Abimelech, which he did unto his father, in slaying his seventy brethren;" — Judges 9:56 (ASV)

Thus God rendered the wickedness of Abimelech which he did
to his father
To the disgrace of his father's character, and to the hurt of his father's family:

in slaying his seventy brethren ;
excepting one, which was a piece of unheard of wickedness, attended with most sad aggravations; the shedding such blood required blood to be shed again, and it was righteous judgment God rendered to him; this, and the following verse contain the remarks made upon this history by the writer of it, who, as we have seen, in all probability, was the Prophet Samuel.