And Yaakov left Be’er Sheva…
(Bereishis 28:10)
This is why Yitzchak blessed Esav that he should “live by the sword” (Bereishis 27:40) — through the mitzvah of honoring his father that he performed using his sword, he merited some power in this world. This is why the verse says, “al charbecha — by your sword” and not “b’charbecha — with your sword” — by way of your sword; because of what you did with it, you shall live.
When the Jewish people wish to weaken the strength of Esav, they need not use the power of all of the 613 mitzvos, since even in the one mitzvah from which Esav draws power, the Jewish people surpass him. The Torah teaches us that Yaakov honored his father more than Esav — the Midrash relates (Targum Yonasan 27:31) that Esav could not find game to hunt so he brought a dog instead and planned to feed that to his father.
This is the meaning of “And Yehoshua weakened Amalek and his nation by the sword” — even by the power of the sword that symbolizes Esav’s one mitzvah of honoring his father, Yehoshua [representing the Jewish people] weakened [and surpassed] Amalek.
This then is the meaning of “And Yaakov left Be’er Sheva [literally, ‘the well of the seven’].” It is known that Be’er Sheva alludes to the high spiritual levels that Yaakov had achieved, since he rectified all the seven character traits, as explained in the holy writings.