Reb Chaim Vital says in the name of the Arizal that there are twelve gates in the Heavens corresponding to the twelve tribes and each tribe has a designated entrance for their prayers. Each gate and their approach are different from the others.
Each of the tribes had their own specific Nusach Hatefillah [specific prayers]. The Holy Arizal established a Nusach that corresponds to all twelve of the tribes. The "Nusach Arizal" are the prayers for those who do not know their tribe.
The Chasam Sofer writes this concept in the name of the Maggid of Mezritz. He explains that in fact, there are thirteen gates in Heaven for our tefillos to pass through. Each gate is for one of the tribes and everyone’s tefillah can pass through the thirteenth gate.