Gemara: [The tav is a sign of] those who kept the entire Torah from aleph to tav.

Ein Ayah: The existence that comes about without self-preparation for the light of Torah and the reasons of the mitzvot follows the order of the Torah. A person can fulfill his Maker’s desire only by doing that which the Torah sets forth. He cannot do it through his own ideas based on secrets of perceived truths from a boundless extension of the Torah’s sanctity.
It is different for one who already was elevated to the greatest heights of Torah understanding and knows his Maker and His intent with the Torah in general and the spiritual power found in specifics elements of Torah and mitzvot. Such a person can use the Torah and mitzvot and their hidden meanings as one uses the letters of the alphabet to represent anything in the world. The Torah is part of their essence and shines even on their external faces. For them, the entire Torah is like letters, which include all the expressions, which are created all the time. This is as the pasuk says: "For Your statutes are to me like speech" (Tehillim 119:99).
Just as there is an order of letters, there is an order of Torah. Both are gathered into units that create new ideas. Anything that is connected to truth and wisdom stems from the light of Torah and proper observance of mitzvot. Scattered ideas constantly combine to create complete ideas that give meaning to everything in the world. These are the people who fulfill the entire Torah from aleph to tav.