Sforno on Genesis 49:30/ספורנו על בראשית מ״ט:ל׳

1אשר 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.