The standard Kelestian cosmology as outlined in canon doesn't do a lot for me. It seems a very "modern" mindset to approach the notion of parallel worlds. I retain it in my own p-Harn as a limited (and unusual) set of theories about the multi-verse. However, the more standard view (accepted by most Shek P'var in one form or another and the majority of the Guild of Arcane Law) is as follows:
A Gnostic Cosmology of Kelestia
Lythian scholars apply the label “Kelestia” to the cosmic all - the sum total of all realities. Within this, they identify a bewildering array of different worlds and universes to which they believe travel is possible. Kethira is the name for both the world on which the continent of Lythia is located (known by most educated folk to be spherical), and also the name given to the reality in which the world Kethira is located.
There are many different cosmological belief systems held by different groups across Lythia. Most of these have some elements in common, but they differ both in the details and in how the main elements relate to each other. The so-called Loresara cosmology was first articulated by the Loresara Gnostics in the principality of Hacherdad in the second century BT. The concept spread to the Azeryan peninsular by the end of the first century TR, and was popular as far west as Melderyn by the end of the fifth century.
While the Nahlic cosmology (named for Nalah Uroh, author of the Libram of the Pantheon) names many distinct worlds (Kethira, Yashain, Terra, Sherem, Losenor, Midgaad, and the Blessed Realm) each distinct from the others, the Loresara Cosmology identifies only two primal realities. One of these, Kethira (sometimes referred to as Kelestia by the Loresarans) consists of an infinite series of realities layered on top of each other. The known, or primary Kethira is thought to lie in the middle of this series. Kethiras “above” Kethira prime are thought to get progressively more perfect until one ultimately reaches the First Gods. In the Loresaran cosmology, the First Gods are sometimes also referred to the “Elemental Spheres” and are thought of as a domain where all the elements of Kethira Prime have been distilled into their most perfect form.
Kethiras “below” Kethira prime are believed to become increasingly entropic until they eventually become one with the void. The Orb of the Bukrai is said by Loresaran mystics to simply be the entropic counterpoint to the Elemental Spheres. Most of the other so-called realities from the Nahlic cosmology (Terra, Sherem, Midgaad, Losenor, and the Blessed Realm) are regarded in the Loresaran cosmology as simply part of the continuum of Kethiras. The Blessed Realm, for example, is a Kethira that lies relatively close to the Elemental Spheres. A traveller there would find it noticeably more perfect in all respects than Kethira Prime. On the other hand, it is far enough from the Elemental Spheres that it does remain recognisably a “world” as opposed to something requiring a higher level of consciousness to even perceive. Losenor, on the other hand, is believed to lie close to the Bukrai. It is a void, but not an empty void by all accounts as it is filled with incandescent gas.
The Loresarans see Yashain as qualitatively different from the various Kethiran realities. There is only one Yashain in the Loresaran cosmology which surrounds and touches upon all of the various Kethiran worlds. The parts of Yashain that lie closest to Kethira are believed to be relatively similar to Kethira. Faya, for example, is taken to be close to the border between Yashain and Kethira. As one moves further away from Kethira, Yashain becomes more and more abstract until, in the outer reaches of Yashain, even abstract concepts may take on tangible forms. Some sages believe that the outer reaches of Yashain fold back on the Elemental Spheres and the Bukrai, and that one can ascend to the highest and lowest realities by traveling “outward” in Yashain as well as by ascending or descending from one version of Kethira to the next.