7. "And these are the generations of Isaac, Abraham's son." Rabbi Yosi asks, What has changed? It did not say, "Abraham's son" previously. For although it is written, "Elohim blessed his son Isaac," (Beresheet 25:11) Abraham is now dead; THAT IS, HE BLESSED AND RAISED THE LEVEL OF ISAAC, WHICH IS GVURAH, AFTER THE DEATH OF ABRAHAM. THUS, the image of Abraham was upon Isaac and stayed with him - WHICH MEANS THAT THE QUALITY OF ABRAHAM, WHICH IS CHESED, REMAINED WITHIN ISAAC - so that whoever saw Isaac said, "...This is surely Abraham," and pronounced that Abraham begat Isaac - WHO WAS INCLUDED IN AND CLOTHED WITH THE QUALITY OF ABRAHAM, WHICH IS CHESED. THEREFORE, THE SCRIPTURE HERE SPECIFICALLY READS, "ABRAHAM'S SON," AS WELL AS, "ABRAHAM BEGOT ISAAC."
7. וְאֵלֶּה תּוֹלְדוֹת יִצְחָק בֶּן אַבְרָהָם. אֲמַר רִבִּי יוֹסֵי, מַאי שְׁנָא דְּעַד הָכָא, לָא כְתִיב בֶּן אַבְרָהָם, וְהַשְׁתָּא אֲמַר, אֶלָּא אע"ג דִּכְתִיב וַיְבָרֶךְ אֱלֹהִים אֶת יִצְחָק בְּנוֹ, הַשְׁתָּא דְמִית אַבְרָהָם, דְּיוֹקְנֵיהּ הֲוָה בֵּיהּ, וְאִשְׁתָּאַר בֵּיהּ בְּיִצְחָק, דְּכָל מַאן דְּחָמֵי לְיִצְחָק, הֲוָה אֲמַר דָּא אַבְרָהָם וַדַּאי, וַהֲוָה סָהִיד וַאֲמַר אַבְרָהָם הוֹלִיד אֶת יִצְחָק.