I realized an interesting connection when reviewing the parshah this week.
When Abraham's servant Eliezer brought Rivkah back with him, they first saw Yitzchak from a distance. Rivkah asked who that man was, and Eliezer replied "It is my master" (Gen 24:64-65). This has always struck me as odd because his master was, of course, Abraham, not Yitzchak. And in fact, several times in the just preceding verses (24:44, 48, 51), Yitzchak is referred to as Eliezer's masters's son, but never directly as his master. So why the sudden apparent promotion?
I think the answer may be very simple: As the midrash on Yayera (21:2) tells us, Abraham and Yitzchak looked very much alike. The midrash on Chayei Sarah further states that the words "Abraham was old, well on in years" teach us that Abraham specifically prayed that he - and subsequently the elderly in general - should show physical signs of old age, so that people could distinguish them and show them the proper respect. But until that point, Abraham and Yitzchak still resembled one another so closely that people had trouble telling them apart.
Thus, when Eliezer spied Yitzchak from a distance, he first thought he was seeing Abraham!