We find regarding food that the refined parts are digested and turn into blood, and the waste parts are expelled from the body. The reason that this filtering is required is because the food derives from a spiritual level called Kelipas Noga also referred to as “The 70 Ministering Angels”.
Tanya chapters 6-8 explains the idea of “kelipas noga”. The word “kelipa” means a “shell” or “peel” covering holiness. Unholiness is defined as something that covers over holiness like a shell covers over a fruit. There are two types of these coverings: kelipas noga and shalosh kelipos hatemeios. Kelipas noga allows some holiness to pass through, like a curtain that allows some light from the sun. This refers to permissible matters, like kosher food. These cover holiness in that attraction to them distracts from seeing the holy potential within, but they allow holiness to pass in that they can be used to serve Hashem. Thus, kelipas noga needs to be refined. The attraction to it for its own sake is discarded, and the holiness it contains is revealed through use in serving Hashem. In contrast, shalosh kelipos hatemeios are three levels of coverings that don’t allow any holiness through. They refer to objects which are forbidden by the Torah and cannot be used to serve Hashem.
In Tanya Igeres HaKodesh chapter 25, the Alter Rebbe explains that all divine energy that comes into the world (at least outside of Eretz Yisrael) comes through the level of the angels called “Ministering Angels Appointed over the 70 Nations”.
Since these angels are themselves spiritually limited, all the divine energy channeled through them is limited to some level of kelipa. All kosher food we eat needs spiritual refinement since it comes from kelipas noga through the medium of these angels.
The words לְבָבְךָ are interpreted by our Sages to mean with emotions of both the Divine soul and the emotions of the animal soul. They learn this out from word “לְבָבְךָ-your heart” which usually has one letter ב' and is spelled לבך, the double letter ב' means double amount of feelings, the emotions of the Divine soul and of the animal soul.
