Why is the word "Nesi'im" written without the second "Yud"?
Rashi: "Nesi'im" means "clouds," 1 and HaSh-m was hinting here that in spite of the Berachos contained in this Pasuk, Yishma'el's twelve tribes will eventually dissipate like clouds.
Gur Aryeh: The Torah could have used the word "Shevatim" (tribes), as it does by Yaakov's children (49:28), yet it chooses the word "Nesi'im."
Why is Yishma'el not alluded to among the "four kingdoms" that would subjugate Bnei Yisrael?
Maharal (Ner Mitzvah, p. 18): The "four kingdoms" include those nations that rose to power by taking it from the Kingdom of Am Yisrael, (and will eventually return it to them). Yishma'el, on the other hand, was blessed with a kingdom in his own right, by virtue of being the son of Avraham.
What is the significance of the opening phrase in the Pasuk, "Regarding Yishma'el, I have heard you"?
Ramban #1: Avraham prayed on behalf of Yishmael because he thought that he would be his only son. 1 But now that HaSh-m was giving him a son from Sarah, he would no longer pray for Yishma'el. Nonetheless, HaSh-m was now informing him, He had accepted his Tefilos on behalf of Yishma'el, and would bless him even after the birth of Yitzchak.
Ramban #2: With reference to what was explained in 17:18 (that Avraham prayed that Yishmael should be a Tzadik), 2 HaSh-m answered him here that He had answered him and that Yishmael would do Teshuvah.
It is unclear what the Ramban means, bearing in mind that when Avraham prayed for him in 17:18, HaSh-m had already told him about the son that Sarah would bear him!
QUESTIONS ON RASHI
Rashi writes: " 'Twelve princes' (Nesi'im) - [for] they will dissipate like clouds, as in the verse, 'clouds (Nesi'im) and wind' (Mishlei 25:14)." What is the significance of this analogy?
Maharal (Netzach Yisrael Ch. 26, p. 133): The Midrash (Eichah Rabah 1:51) writes that Mashi'ach will be born in "Biras Araba" (which the Maharal connects to "Arabia"). Mashi'ach is also described as "on the clouds" (Daniel 7:13; Rashi loc. cit). Bnei Yishma'el are called "Nesi'im," for they seem to rise ever upwards, but will finally dissipate. Mashi'ach will arise and become uplifted over them. 1
Maharal (Chidushei Agados Vol. 3, p. 216, to Sanhedrin 98a): The Pasuk describes Mashi'ach as "arriving on the clouds." Although they may be lofty, clouds are associated with Chomer - they consist of water, they have no fixed shape (Tzurah), and are short-lived. If we are worthy, Mashi'ach will "ride upon the clouds" - i.e. be over and above even more lofty aspects of Chomriyus (physicality).