Or HaChaim on Genesis 27:1/אור החיים על בראשית כ״ז:א׳

1 ויהי כי זקן יצחק, It came about when Isaac was old, etc. The reason that the Torah prefaces the paragraph by reporting that Isaac's eyesight failed him was to explain that Jacob took the blessings at a time when he was not afraid that his father would recognise him. The reason the paragraph is introduced with the word ויהי, which always introduces a painful episode, is to remind us that the subterfuge Jacob had to employ had many fateful consequences for the history of the Jewish people.

2את עשו, Esau. The reason the Torah does not say ויקרא אל עשו, that Isaac called out to Esau, is that the latter was not present. Isaac merely called out Esau's name.

3בנו הגדול, his older son. The Torah may have given as the reason that Isaac called first on Esau the fact that he was the firstborn; this would presuppose that Isaac did not know about the sale of the birthright. Alternatively, Isaac may have ignored the fact of the sale of the birthright and have based himself on Esau's being the elder, biologically speaking. The reason that Isaac wanted to give the wicked Esau a blessing was that he hoped to effect a change in Esau's character on account of the blessings he would bestow on him. In view of the statement in Bereshit Rabbah 80,1 that Dinah's rape was a punishment for Jacob who had hidden her from Esau's view at the moment of reconciliation, thus preventing Esau from marrying her, we may assume that had Rebeccah and Jacob not interfered with Isaac's intention Esau might indeed have become a penitent as a result of receiving such a blessing.