What is the significance of the Tefilah here?
What is the significance of the Name 'Keil Shakai' here?
Rashi #1: 'Kel Shakai' means, He Who is sufficient in dispensing His mercy, and Who has sufficient ability to give. (Gur Aryeh - This explains why Yaakov prayed by invoking this specific Name of Hashem.)
At the creation, when He ordered the world to stop expanding (after it reached the size of 500 years' journey - Hadar Zekenim).
Since his youth, Yaakov's troubles had never ceased - Lavan, Esav, Rachel, Dinah, Yosef, Shimon and Binyamin. Da'as Zekenim - His troubles started in the womb (Esav fought with him)!
If "Es Achichem" refers to Shimon, to whom does "Acher" refer?
Rashi: A spark of Ru'ach ha'Kodesh entered into Yaakov, and he hinted that Yosef was about to be returned to him. 1
Ramban (citing the Midrash): The entire Pasuk refer to the Galus and the Ge'ulah -- "ha'Ish" refers to Ha'Kadosh-Baruch-Hu; "Es Achichem," to the Ten Tribes, and "Acher v'Es Binyamin" to Yehudah and Binyamin. "Ka'asher Shacholti" - with the destruction of the first Churban Beis-ha'Mikdash; "Shachalti" - with the destruction of the second Beis-ha'Mikdash (but I will not be bereaved again). 2
Why did Yaakov not mention Shimon by name?
Ramban: Because he had not yet forgiven him for what he did to Shechem 1 (and he presumed that it was on account of that sin that Shimon had been incarcerated). 2
Ramban: As a matter of fact, had it not been for the shortage of food, Yaakov would not have sent the brothers back to Egypt in order to get back Shimon.
Probably assuming further that Shimon was the instigator and that Levi only followed suit (just as Yosef actually incarcerated him and not Levi - because he had instigated throwing him into the pit).
What did Yaakov mean when he stated, "Ka'asher Shacholti, Shachalti!"?
Rashi and Targum Yonasan: Just as 1 I have been bereaved from Yosef and from Shimon, so too will I be bereaved from Binyamin. 2
Ramban: 'I am bereaved anyway and I cannot be more bereaved than I am!' 3
Rashbam: I am sending Binyamin with doubts in my mind; and whatever will be, will be. 4
Ibn Ezra: As I was bereaved from Yosef, it is considered as if I am bereaved from everything.
Malbim: My Mazal turned bad from the loss of Yosef. I do not hope for mercy in my merit. Your Mazal did not worsen. Hashem should do (give mercy to you) in your merit!
Ha'amek Davar: I was bereaved from Yosef. I planned to make two tribes from him. It is as if I am bereaved from two!
Targum Yonasan writes "if" in place of 'just as.'
Rashi: Bereaved out of doubt, until your return. Gur Aryeh - It is not that Yaakov was certain that tragedy would befall them on the way; after all, he had prayed for them!
Ramban: Like Esther said, "Ka'asher Avadti, Avadti!" (Esther 4:16).
Rashbam: Like Esther said, "Ka'asher Avadti, Avadti!" (Esther 4:16).
Why does it say, "v'Shilach Lachem Es Achichem Acher"?
Ha'amek Davar: Yaakov suspected that Shimon was incarcerated because he was at odds with his brothers. Now that he was incarcerated, he repented, and he will be like a new man, and pleasing to you.