I have given all the separated portions of the sanctified animals that the Israelites set aside for G-d to you [Aaron] and your sons and daughters with you, as an eternal portion. It is an eternal covenant of salt before G-d for you and your descendants with you.
Numbers 18:19
The Torah’s outer dimension is the knowledge of how G-d wants us to live our lives in the context of our physical world. This knowledge is contained in the Talmud and its associated legal texts.
The Torah’s inner dimension is the knowledge of the inner life of the soul and its spiritual relationship to G-d; this knowledge is contained in the texts of Jewish mysticism (Kabbalah) and in the vast corpus of Chasidic teachings.
Allegorically, the Torah’s outer dimension is compared to bread and meat, the staples of a healthy diet, since we must study this dimension of the Torah in order to lead a healthy spiritual life.
In contrast, the inner dimension of the Torah is compared to salt, which enhances the taste of the food it touches. Including the study of the inner dimension of the Torah in our spiritual “diet” reveals the intrinsic sweetness of the Torah’s outer dimension.
--Daily Wisdom Volume 3