Why does the Torah use double expressions, "Ki Varech Avarechecha" and "v'Harbeh Arbeh"?
Rashi: One is for the father (Avraham) and one for the son (Yitzchak). 1
Mishnas R. Aharon (Vol. 3, p. 171): This Berachah was said in the place of the Mikdash (in the territory of Binyamin). Therefore, Binyamin increased tremendously. After Pilegesh b'Giv'ah, only 600 men remained, and yet in the days of Yehoshafat there were already 380,000 soldiers from Binyamin! Yehudah was nearby, and also increased greatly (Divrei ha'Yamim II 17: 14-18).
QUESTIONS ON RASHI
Rashi writes: "I shall surely bless you (Barech Avarechecha) - one [blessing] for the father (Avraham), and one for the son (Yitzchak)." But the Torah frequently utilizes a double expression in the infinitive; why expound on it specifically here?
Gur Aryeh: When the verse warrants it, we may expound from a doubled expression. In this case, surely Yitzchak was also deserving of blessing for his role in the Akeidah. Chazal derive his blessing from the doubled expression.
