ועקדת יצחק לזרעו היום ברחמים תזכור
The Shulchan Aruch (O.C. 591:7) says this is the correct nusach and not the nusach that adds the name of Yaacov (in order not to include Yitzchak’s children which includes Eisav).
The nusach can be understood according to the Medrash about Tehilim (22, 24) הללוהו כל זרע יעקב כבדוהו, וגורו ממנו כל זרע ישראל. The Medrash explains that the first part of the verse refers to the 11 sons of Yaacov, and the second part of the verse refers to Binyomin son of Yisrael. Eleven sons were born when he was known as Yaacov, and only Binyomin was born when he was called Yisrael.
Thus, the above phase cannot refer to Yaacov nor refer to Yisrael since either would not include all of the Jewish tribes. Thus, the verse leaves the word without specific reference, just זרעו.
As a side note, one can understand the verses in Parshas BeShalach:
- (שמות יד,טו) דבר אל בני ישראל ויסעו
- (טז) ויבאו בני ישראל בתוך בים ויבאו בני ישראל.
The second B’nai Yisrael seems extra. The second half of the verse also refers to the entering into the sea. Thus, the second B’nai Yisrael refers to the tribe of Binyomin (and not Yehudah) that had the merit to be the first tribe to enter into the sea. This reflects that Binyomin was the honored one of the sons that he was born to Yisrael, who wrestled with angels and prevailed.
