וַיָּבֹ֤א יַעֲקֹב֙ אֶל־יִצְחָ֣ק אָבִ֔יו מַמְרֵ֖א קִרְיַ֣ת הָֽאַרְבַּ֑ע הִ֣וא חֶבְר֔וֹן אֲשֶׁר־גָּֽר־שָׁ֥ם אַבְרָהָ֖ם וְיִצְחָֽק׃
And Jacob came unto Isaac his father to Mamre, to Kiriatharba—the same is Hebron—where Abraham and Isaac sojourned.
Sforno on Genesis
Where Avraham and Yitzchok lived. Righteous forebears stand a person in good stead among his neighbors.
Radak on Genesis
ויבא..קרית הארבע, we explained the meaning of this on 23,2. The reason for the definitive article in front of the word ארבע, i.e. הארבע, something strange seeing that it refers to the name of a human being, is justified as the name itself is symbolic, i.e. is in reality an attribute, describing the “foursome,” the father and his three sons, all of whom giants.