When praying on behalf of Yishma'el, why did Avraham add the word "Lefanecha (before You)"?
Rashi: The word "Lefanecha," when it refers to HaSh-m, means "with Yir'as Shamayim." 1
Targum Yonasan: It means that "he should (live and) worship You."
Ramban: Avraham was praying that Yishmael should live, and that his offspring should live as long as the world lasts.
Seeing as HaSh-m just promised Avraham that he would have a child from Sarah, why did he pray for Yishma'el?
Ramban: Until now, Avraham believed that HaSh-m's promise (15:4) that his own child (and not Eliezer) would inherit him, referred to Yishmael. Now that HaSh-m informed him that in fact, it referred to Yitzchak, he was afraid that Yishmael would die. Therefore Avraham declared that he only accepted the new Berachah if Yishma'el's progeny will endure.
QUESTIONS ON RASHI
Rashi writes: "If only Yishma'el will live; [for] I am an unworthy of such a reward!" How is this implied in the Pasuk?
Gur Aryeh: The literal meaning would be that Avraham feared that Yishma'el would perish; but why would that be? Rather, Avraham was expressing his feeling of unworthiness of this gift. 1
Rashi writes: "[If only Yishma'el] would live before You - i.e., as G-d fearing." Ramban asks - can this have been Avraham's request? HaSh-m responds, "Regarding Yishma'el, I have heard [your request...]" (17:20); yet we do not find that Yishma'el became G-d fearing?
Gur Aryeh: Avraham could not have asked directly that Yishma'el should fear HaSh-m. Fear of HaSh-m is the task of every individual. Avraham merely asked that Yishma'el live, and thus have the opportunity to serve and fear HaSh-m; and this is what HaSh-m granted.