פירוש על בראשית 27:29

בני אמך THY MOTHER’S SONS — Jacob, however, said to Judah (49:8) “Thy father’s sons (shall bow down to thee]”, because he had sons by several wives, but here, because he (Isaac) had but one wife he said “thy mother’s sons” (Genesis Rabbah 66:4).

CURSED BE EVERY ONE THAT CURSETH THEE, AND BLESSED BE EVERY ONE THAT BLESSETH THEE. But in the case of Balaam it says, Blessed be every one that blesseth thee, and cursed be every one that curseth thee.²²¹Numbers 24:9. The question thus arises: Why did Isaac mention first the curse and then the blessing while Balaam did the opposite? [The reason for this change in order is that] the righteous begin with affliction and ultimately attain tranquility, so that those who curse them precede those who bless them.²²²Therefore, Isaac, himself a righteous man, speaks first of those who afflict the righteous, and then mentions those who bless them. The opposite is true in the case of Balaam. But the wicked experience tranquility first and their end is affliction. Hence Balaam mentioned the blessing before the curse. This is Rashi’s language quoting Bereshith Rabbah.²²³Bereshith Rabbah 66:5.
But if this be so, why did the Holy One, blessed be He, say to Abraham, And I will bless them that bless thee, and curse him that curseth thee?²²⁴Above, 12:3. Now here in the case of the righteous, it still mentions the blessing first! This however is no difficulty since He concludes there, And in thee shall all families of the earth be blessed. Thus there is a blessing at the beginning and at the end. It may be, as we have explained it there, that He speaks in terms of both an individual and many,²²⁵The blessing is expressed in plural form — And I will bless ‘those’ who bless thee — while the curse is expressed in singular form — and curse ‘him’ that curseth thee. suggesting that Abraham will be universally blessed, and the single person who will curse him will be cursed.²²⁶Hence He mentions the blessing first as there will be many who will bless Abraham.

בני אמך, here the word וישתחו appears in the singular, whereas in a parallel blessing pronounced by Yaakov who had several wives (Genesis 49,8) the word וישתחוו appears in the plural.