בַּמְּעָרָ֞ה אֲשֶׁ֨ר בִּשְׂדֵ֧ה הַמַּכְפֵּלָ֛ה אֲשֶׁ֥ר עַל־פְּנֵי־מַמְרֵ֖א בְּאֶ֣רֶץ כְּנָ֑עַן אֲשֶׁר֩ קָנָ֨ה אַבְרָהָ֜ם אֶת־הַשָּׂדֶ֗ה מֵאֵ֛ת עֶפְרֹ֥ן הַחִתִּ֖י לַאֲחֻזַּת־קָֽבֶר׃
in the cave that is in the field of Machpelah, which is before Mamre, in the land of Canaan, which Abraham bought with the field from Ephron the Hittite for a possession of a burying-place.
Rashbam on Genesis
לאחוזת קבר, they will not be able to challenge my right to be buried there.
Sforno on Genesis
אשר קנה אברהם, seeing that they had already spent many years in a foreign land, he felt it necessary to remind them that that burial plot was legally theirs. Seeing that already two generations of the patriarchs had been buried there, there was no legal way anyone could now challenge the ownership of this cave.
Radak on Genesis
במערה, we have explained on Genesis 25,10 why this mention of the cave of Machpelah as the patriarchs’ burial site is mentioned so many times in the Torah as if we did not know already.