Judaism: Dvar Torah for Lekh Lekha
And I shall bless those that bless you.
This is but one of many examples of Hashem’s aid to Abraham; why was this example chosen?
Because one who attempts to contradict the majority of men must expect a torrent of reproach and vilification; therefore Abraham had been exposed to much animosity and he was cursed by the rulers and the priests and by the multitude of their followers.
This was a prophetic parallel to Abraham’s seed that opposed the idolatrous and cruel and immoral nations, and that opposed the false religions and the materialists, and were therefore the target of a torrent of vilification.
For this reason G-d promised to take action against the defamers of Abraham’s seed. The cursers would be many, but in the end Abraham’s name remained blessed by all. Thus it would be with his seed (see 32:30). "And their seed shall be known among the nations, and their offspring among the people; all that see them shall acknowledge them, that they are the seed that Hashem has blessed" (Isaiah 61:9).
From the statement in Hullin (49 A) it is evident that this promise to bless him extends also to his descendants:
"Rabbi Akiva says: We learn that the Cohanim bless Israel; and by the words ‘And I shall bless them’ (Bamidbar 6:27) we learn that the Holy One blessed be He confirms their blessing." The Talmud then inquires: "From where do the Cohanim gain their blessing? Said Rav Nachman bar Yitzchak: From ‘I shall bless those that bless you’."
This implies that this promise extends to all descendants of Abraham, even to individuals.
From this statement of the Talmud we learn also that not only when non-Jews bless Israel will Hashem bless them, but also when Jews (such as Cohanim, or anyone else) bless Jews they gain a blessing.
The same therefore would be true if a Jew cursed a Jew, and those that curse you I shall curse."