פירוש על בראשית 12:3

ונברכו בך AND IN THEE SHALL BE BLESSED — There are many Agadoth concerning this but the plain sense of the text is as follows: A man says to his son, “Mayest thou become as Abraham”. This, too, is the meaning wherever the phrase ונברכו בך “And in thee shall be blessed” occurs in Scripture, and the following example proves this: (Genesis 48:20) בך יברך “By thee shall Israel bless their children saying, “May God make thee as Ephraim and Manasseh”.

ונברכו, a composite, from the word מבריך, מרכיב, refining through adding superior ingredients. The Torah chose a passive mode to express this blessing.

ואברכה מברכך, I shall bless those who bless you. This additional blessing was to compensate Abraham for G'd's failure to tell him the destination he was headed for. After all, G'd did not even tell Abraham which country to head for! It was a tremendous test for Abraham to just leave his home, etc., without having the slightest idea where he was to make his new home. The fact that Abraham did not query G'd in his mind or by prayer is considered as extremely praiseworthy. As a result of this blind faith in G'd, Abraham encountered success wherever he went. His spiritual stature grew constantly.