Why does the Torah use the double expressions "Ki Varech Avarechecha" and "ve'Harbeh Arbeh"?
Rashi: One is for the father (Avraham) and one for the son (Yitzchak). 1
Mishnas R. Aharon (3 p.171): This Brachah was said in the place of the Mikdash (Binyamin) Therefore, Binyamin increased tremendously. After Pilegesh b'Giv'ah, only 600 men remained, and in the days of Yehoshafat there were already 380,000 soldiers from Binyamin; Yehudah was nearby, and also increased greatly (Divrei ha'Yamim 2:17:14-18).