The answer to this will be from the analogy of a person’s hair, which derives its life from the brain, even though, in the brain itself, there is nothing similar to hair. Nonetheless, the brain can condense its own life-force and direct it towards enlivening the hair.
We see two opposites with regard to the life of the hair: On the one hand, it has less life than the rest of the body, which is why it doesn't hurt to cut the hair, since it has so little life-force. On the other hand, it grows close to the brain, so the minimal life that it does receive has the quality of having a special connection to the brain, more so than the rest of the body (below the head).
So, too, with regard to the Torah and Mitzvos, even though they are expressed in physical matters, which are far removed from the way they exist purely spiritually, in Hashem’s Will and Wisdom, nonetheless, “the Torah came forth from Hashem’s lofty spiritual Wisdom” and is still connected to its source, just like the lifeforce in the hair, which is still connected to its source in the lifeforce of the brain.
Just like the life in the (attached) hair is still connected to the life of the brain, which is its source, despite the great contrast between them, so, too, the Torah and Mitzvos are still directly connected to their source in Hashem's Essential Will and Wisdom. Therefore, they can connect the person directly to Hashem’s Will and Wisdom, which is totally beyond the limitations of the world and of human understanding.
Completely unified with Him to the extent that they unite the one who learns and fulfills them with Hashem? This is what the Alter Rebbe will proceed to explain with an analogy from a person’s hair.
