Why did Avraham add the word "mi'Lefanai", considering that, at that moment, Sarah was not lying in front of him?
B'rachos, 18a: This teaches us that an Aveil who is obligated to bury his deceased is Patur from all Mitzvos, even if the deceased is not actually lying in front of him
Rashi (in B'rachos, 17b): Who is Patur because his mind is busy with the Mitzvah of burying the deceased.
Why does it say "Bnei Ches" 10 times?
Da'as Zekenim: This shows that one who helps to clarify the portion of a Tzadik, it is as if he fulfilled the five Chumashim.