Or HaChaim on Genesis 35:12/אור החיים על בראשית ל״ה:י״ב

1 לאברהם וליצחק, to Abraham and Isaac. Check on what we have written on Genesis 26,3 that the promise G'd made to Isaac concerning inheriting the land of Israel contained an additional dimension to the promise made to Abraham. G'd promised this additional dimension also to Jacob.

2אתן את הארץ. "I shall give the land." Why did the Torah have to mention the word "the land" once more instead of simply saying "it," as the Torah did at the beginning of this verse? Perhaps the Torah wanted to tell us that G'd would give this land to Jacob in order that he personally should possess it, not merely his descendants. Had the Torah merely written לך אתננה ולזרעך, we would have understood that Jacob could only make the claim to the land over to his children as an inheritance. This is why the Torah speaks of two separate gifts here, one to him and one to his descendants. This had not been the case when G'd promised the land to either Abraham or Isaac.