Gemara: [We saw last time that Rav arrived in Bavel from Eretz Yisrael, and Shmuel sent Karna to get an impression of Rav’s greatness.] He went and found Rav and said to him: How do we know that tefillin can be written only on the hide of a kosher animal? Rav answered: For it is written: "So that the Torah of Hashem will be in your mouth" (Shemot 13:9), which teaches that it must be [written] on something that you are allowed to put in your mouth.

Ein Ayah: The most spiritually elite among the Jew’s of Bavel were connected to the love of Eretz Yisrael with all their hearts. These people always wanted to express that they appreciate the Holy Land. Discussion of the great value of the sanctity of Eretz Yisrael is a recurring theme, which we see appearing, scattered in many sections of the Babylonian Talmud. This goes together with the recognition that living in the Diaspora is a negative thing even if the situation there is ostensibly good, whether it be in relation to the Jewish community’s physical welfare or its spiritual level.

At the end of the story, that which sustains the nation is the Land, and exile, with its impure ground, must by necessity, harm the light of the Torah’s sanctity and all of the highest spiritual levels that exist within the nation. When the Holy Land is given the opportunity to sustain the nation, it will possess the light of sanctity.

The sign for these concepts is the hide upon which matters of sanctity are written. They must not be written on impure hide even if they are prepared in a very pleasing way, because sanctity cannot connect to an impure material. Similarly, the sanctity of the soul, connected to the light of the Jewish nation, cannot be connected properly with a community of people who are living in an impure land. [Karna was] hinting that only a very pressing situation could have caused the departure of someone like Rav from Eretz Yisrael in favor of Bavel. One must posit that there is an eternal advantage of living in Eretz Yisrael, the Holy Land, the place of the highest sanctity and purity.

Rav also responded in a similar vein. He said the reason that tefillin must be written on the hide of a kosher animal is that the Torah must be written on something that is permitted to put in one’s mouth. Even though the Torah portions are written on parchment, which is not a part of the animal that one eats, still the material that is the base for the words of Torah must be pure. So too, the land to which the sanctity can be connected to the Jewish people must be a holy land, a land which was given to us to eat its fruit and be satiated from it. In that manner, both the body and the spirit are nourished, as both elements are connected in the chain of the light of Torah, which shines only in the place that Hashem desires to dwell. This is not true in a land of darkness, where the light is not powerful enough to properly sustain the Jewish nation in exile. This is true even in a time when the Jewish people need to be in the Diaspora until the appointed time.