Suares: Dallet-Mem-Tav (4.40.400): the physical resistance of structures, Dallet (4) finds its purveyor in the
maternal waters, Mem (40), where all life originates. Tav (400) is the exaltation of the entire cosmic existence in its
utmost capacity to resist to life-death. The root Dallet-Mem (Dam) is "blood" in Hebrew and the root Mem-Tav (Met)
is "death." Thus the two together express the complete cycle of existence.
Tav (Double Letter): spelled Tav-Vav: 400-6: Cosmic resistance -- fertility: infinite beyond space-time compressive energy, opposite to Aleph's outside of space-time infinite expansive energy. Tav is the perfectly hard cosmic mirror that reflects Aleph back equally and oppositely, establishing and maintaining a double current or flow of structuration on all levels of matter and spirit. This is, of course, the secret of the Qabala in its final, most concise form: Aleph-Tav are one and create all that is. See Jacob's Ladder.
Tav (Tav-Vav) is the only letter with Vav as a single root besides Vav itself (Vav-Vav). Vav connects ("ands") other letters. Tav connects with all the letters, being the ultimate sanctuary of their energies.
The life of Aleph (Aleph-Lammed-Phay-Hay) is reflected back in the fertility of Tav (Tav-Vav). In return, all the Autiot fertilize Tav through Aleph and Yod.
Tav, as the projection of the archetypal "door" of Dalet, is the cosmic door of life-death to the transcendent energies of realized life beyond space-time: the five final letters that complete the last level (500-900, final Kaf through final Tsadde). Here is the location of the door in three-dimensions: