In Genesis 25:21 Isaak intercedes before God “on behalf” of his wife Rivkah on account of her infertility. וַיֶּעְתַּ֨ר יִצְחָ֤ק לַֽיהוָה֙ לְנֹ֣כַח אִשְׁתּ֔וֹ כִּ֥י עֲקָרָ֖ה הִ֑וא וַיֵּעָ֤תֶר לוֹ֙ יְהוָ֔ה This verse, as any verse in Torah, carries in itself the multiple layers of meaning since the simple explanation of what is happening is too shallow and lacks the surgical precision of the Torah language.
The A -B – A structure of the sentence presents a mirror-like construction where Isaak entreats God and, as a result of his plea, God is entreated by him, In the center of this construction is the singular and the most important reason for this plea – Rivka’s infertility.
However, the middle part can also be broken down into two segments – לְנֹ֣כַח אִשְׁתּ֔וֹ and כִּ֥י עֲקָרָ֖ה הִ֑וא. The scheme, therefore, can be expanded to A1 – plea, B1 – reference to the object of God’s help, B2 – a reason for a plea, A2 – result.
The Torah commentators, being aware of this construction, were puzzled by the B1 part which uses the word “opposite”, “on the other side of”. The rabbis differ on whether this means that Isaak himself was infertile or whether he, as Chizkuni states, was praying on behalf of Rivkah, since he was the son of the righteous man and she was the daughter of the wicked.
Bekhor Shor, Joseph ben Isaac Bekhor Shor of Orleans, supporting the view, offers a very beautiful and poignant explanation of Isaac’s action. He knew he was fertile and knew that somebody else could give birth to his child. However, he did not want anyone except Rivkah to be the mother of his future offspring. “For this Yitzchak trusted for himself, but he wished to be built up from Rivkah”. Isaac’s prayer is truly an expression of shared pain. Even though he might be fertile himself, his wife’s happiness matters for him most.