Throughout Chumash Breishit we can find Eretz Yisrael as a central part of the drama. Ever since Avraham Avinu started his journey from Charan, it is clear that the only place for him and his descendants is Eretz yisrael. It is the promised land in which the future nation will prosper, and its landscape is a crucial part of the making of the nation. Leaving that land will be acceptable only if there is no other choice. Avraham found himself going down to Egypt because of the drought, and his grandson Yaakov did the same for the same reason. That is what makes it so unusual that Hashem did not allow Yitzchak to do the same.
But even more than Hashem’s refusal, the reasoning for the decision seems awkward -
'עקב אשר שמע אברהם בקולי וישמור משמרתי מצוותי וחוקותי'.
Why is the fact that Avraham Avinu was faithful and obedient relevant to the decision?
In the Midrash (בראשית רבה) Chazal learn from this pasuk that Avraham Avinu and all the other Avot maintained/followed the entire Torah even though it had not yet been given to them. Chazal even learn from this pasuk that they knew not only the Torah She’Bichtav (written Torah) but also the Torah She’Baalpe (Oral Tradition), meaning that they knew and fulfilled even late Drashot and Takanot that Chazal established over the years.
Relying on those teachings, the Ramban points out a very fascinating explanation to our question. He explains that Hashem decided to forbid Yitzchak from leaving Eretz Yisrael specifically because he and his father were so obedient. According to the Ramban, every Mitzva performed in Eretz Yisrael is much more significant than performing the same mitzvah in any other place in the world. Performing a mitzvah in Eretz Yisrael isn’t only doing something suited to the nature of the human being, but doing something completely fitted to the nature of the land.
Eretz Yisrael is the land capable of upholding the high values and the unique spirituality that the Torah and mitzvot stand for, and for that reason any mitzvah performed there is much richer and deeper.
When convincing Yitzchak to stay in the land of Israel Hashem is revealing the plain and simple fact that this is the most meaningful place to be in. Yitzchak Avinu who’s Mida is Din, symbolizes accuracy and punctuality and therefore he should fight the odds despite the difficulty. Yitzchak shows us the way to a natural and precise life willing to challenge difficulties in order to still live in the most pure and suited atmosphere - Eretz Yisrael.