How could Sarah’s tent have remained empty until Rebekah came on to the scene?
Nachmanides and Sforno tell us that out of respect to Sarah’s memory, her tent was left unoccupied until Isaac found a wife. The tent was reserved for her while she was alive, and after she died her loss was evident to everyone.
There is a parallel in modern-day Jewish life when a parent dies and their synagogue seat is left unoccupied for the time being. In Sarah’s case, it was not only the absence of her personality but her piety that left the family and tribe bereft.
The rabbis say (see Rashi’s commentary) that as long as Sarah lived, there was a light burning from one Sabbath eve to the next; the dough was blessed; and a Heavenly cloud hovered over her tent. The light of her words, her thoughts and her emotions illumined the tent; the meals and family feeling were exceptional; and she brought the presence of God wherever she went.
She would have been proud to know that Rebekah was a woman in her own mould.