When Yaakov went to מצרים, the Torah records (בראשית מ"ו:א) that Yaakov offered Korbanot to the God of his father, Yitzchak. There is a question raised by many מפרשים including Rabbis of the Gemara (מדרש רבה צ"ב:ה). Why is Avraham not mentioned? It would seem that Pasuk should have said, ויזבח זבחים לאלקי אביו אברהם ואלקי אביו יצחק (see בראשית לב:י, where Yaakov address his Tefilah to both the God of his father, Avraham and the God of his father Yitzchak).
Rashi, following the opinion of Rabbi Yochanan (בראשית רבה צד:ה), answers that only Yitzchak is mentioned because חייב אדם בכבוד אביו יותר מכבוד זקנו, meaning that one is obligated to honor one's father more than one's grandfather. Yitzchak's relationship with his father was extra special. On the other hand, the Sforno answers that only Yitzchak is mentioned because Yitzchak was forbidden by Hashem to leave Eretz Yisrael and not Avraham. This expresses how upset Yaakov was that he was not like his father. He wished that he would have had the merit his father Yitzchak had, not to leave Eretz Yisrael. This shows that even when a Jew must leave Eretz Yisrael he should feel terrible about doing so (see רש"י שם מו:ג). A Jew should feel deep disappointment about losing his best opportunity to be close to Hashem.