The Tapestry was the Atlantean concept of the world as a whole, before it was fragmented.
Today, the Tapestry is divided in the Lower Depths, the Fallen World (which is further divided into the Material Realm and the Realms Invisible) and the Realms Supernal. Their division was created through the hubris of the Exarchs and the Celestial Ladder which shattered reality and allowed the Abyss to seep into being. The forces of the 10 Arcana bind these different Realms together and maintain stability and order.
During the time of Atlantis, mages thought of the 10 Arcana as threads that created the known worlds. Only by understanding the threads could a mage weave them into Patterns of his own devising. The Atlanteans also pondered the reasons behind their art. They knew with certainty that there was more to reality than what met the common eye, and that there was more than one state of existence beyond the material. They believed that behind the many forms and shapes of things, the world was in fact One, heaven and earth together in a single continuum. Subtle veils divided the realms and states of being from one another, separating high from low and creating the illusion of division. Through Ascension, a mage was able to transcend this illusion and become a being of all Realms by returning to the supernal fires that created everything.