פּירוש אויף בראשית 27:40

ועל חרבך—The phrase is equivalent to בחרבך BY THY SWORD. The word על is sometimes used instead of the prefix ב, as (Ezekiel 33:26) “Ye stand by your sword (על חרבכם)”, which is the same as בחרבכם; (Exodus 6:26) “by their hosts (על צבאותם), which is the same as בצבאותם.

ועל חרבך תחיה, “you will live by grace of your sword.” Yitzchok promises Esau that as a reward for having hunted deer in order to bring him delectable food, he will also henceforth be able to survive by his sword in his dangerous vocation. [The word “sword” here is used by Yitzchok as a general term for instruments used to kill, seeing that Esau had hunted for him with bow and arrow. Ed.]

והיה כאשר תריד, “it will come to pass when you will break loose; (the most common translation, rejected by our author);” (the root רדה, meaning “to subdue) occurs again in Numbers 24,19, in Bileam’s blessings, when that prophet predicts that eventually a time will come when the descendants of Israel will subdue the descendants of Esau, and that at that time Esau’s descendants will accept Yaakov’s yoke willingly.