Chasidut do Rodzaju 18:10

Another way of looking at our verse is that of the ‎‎Ari’zal, who sees in the words ‎כי ביצחק‎ in Genesis 21,12 a ‎reference to the “feminine” side of Yitzchok in the diagram of the ‎‎10 emanations, i.e. the earthly element, seeing that the angel had ‎said to Avraham (Genesis 18,10) ‎והנה בן לשרה אשתך‎, “and here ‎your wife Sarah will have a son.” [The angel emphasized Sarah as ‎predominant in Yitzchok’s birth, not his father Avraham. Ed.] ‎However, subsequently he would receive a soul contributed by ‎Avraham, Avraham representing the masculine element of the ‎chart of the emanations. This point is made by the Torah here ‎repeating what otherwise would be assumed, that Avraham begot ‎Yitzchok. The Ari’zal’s comment also coincides with the ‎meaning of Bereshit Rabbah 58,5 in which the Midrash, ‎referring to Genesis 23,3 where Avraham is reported as “arriving” ‎in order to bury Sarah, asks: “where did Avraham arrive from? ‎Where had he been previously?” One of the answers given by the ‎Midrash is that Avraham came from Mount Moriah. The ‎‎Midrash adds that Sarah died as a result of the anguish she ‎experienced when told that Yitzchok had been slaughtered. She ‎had found this incompatible with G’d’s promise to Avraham that ‎ברך אברכך והרבה ארבה את זרעך‎, “I will continuously bless you and ‎greatly multiply your descendants” which G’d had said to ‎Avraham in Genesis 22,17.‎
At this point the author attributes to this Midrash a ‎third answer to the question whence Avraham came to arrange ‎Sarah’s funeral. I have not found this in any of my editions, ‎although this is the answer that would tie in with our verse ‎above. The Midrash supposedly views as Avraham “coming” ‎i.e. contributing the soul to Yitzchok as alluded to in the words ‎‎(Genesis 21,12) ‎כי ביצחק יקרא לך זרע‎.‎