Celestial Spheres and Philosophies 
Most celestials champion a particular Sphere, and depending upon their choice of how best to use their Celestial Ways, sometimes adhere to a Philosophy. This is not to say that the Sphere or Philosophy dictates or demands specific actions or behaviors; they are guidelines that present ways a particular celestial could find their calling within the Host. Each Sphere is guided by a Primarch, one of the greater Celestial beings that issues orders and commands to the Celestial Host. There are more Primarchs than there are Spheres, and power amongst the Primarchs is not determined by which guide Spheres and which do not. The Primarchs simply view this as one of their ordained duties.
The Spheres
Sphere of Power:
Those within this sphere are focused on the channeling and release of spiritual energy, and sought to perfect their understanding of the Realms of Energy and the presence of the Realms both in the Celestial Halls and the mortal world, even to places beyond. The Primarch Tharamon guides this Sphere.
Celestials belonging to the Sphere of Power pay two fewer points for Magic Sense or Medium. They only receive this price break once.
Sphere of Guardianship:
This sphere promotes protection and guardianship of an ideal, place, or even another person, but is usually broader than scope than a single individual. Home to many warriors, the Primarch Malanariel guides this Sphere; Erialian, the leader of the Vanguard of Oriset, is a high-ranking member of this Sphere.
Celestials belonging to the Sphere of Guardianship may begin play with Wear Light Armor for no cost, or receive a two point price break on Wear Medium Armor or Wear Heavy Armor. They only receive this price break once.
Sphere of Healing:
Mastery of this sphere is not limited to the physical body, but to spiritual and mental restoration as well. The Primarch Calithra guides this Sphere.
Celestials belonging to the Sphere of Healing pay two fewer points for Healing Ways or Chirurgery. They only receive this price break once.
Sphere of Thought:
Celestials within this sphere look to perfect the mind; they are concerned with the overcoming of fears, the receipt of inspiration, and of self-perfection. Many warriors are also of this Sphere.
Celestials belonging to the Sphere of Thought pay two fewer points for Pain Resistance, Strong Will, or any Acute Sense. They only receive this price break once. The Primarch Liath guides this Sphere.
Sphere of Art:
Encompassing all that is creative; this sphere oversees not only creation of works, but also the natural works of the world and the Celestial Halls. They seek to understand not only the Realms of Energy, but the Forms of Matter as well, and how they interact to create things wholly different and beautiful. The Primarch Haladal guides this Sphere.
Celestials belonging to the Sphere of Art pay two fewer points for any Craft or Lore skill for one single level. They only receive this price break once.
The Philosophies
The Celestials, being creatures of order, naturally seek to align themselves with those of like mind. As such, a number of philosophies circulate within the Celestial Halls. These philosophies are often named after important figures within the Celestial Host, or after the Primarchs who most embody such philosophies. These are not the only philosophies of the Celestials, but are among the most common. Not all Celestials feel the need to belong to a philosophy, and no one forces them to adopt one. Those seeking to embrace their Celestial natures once they descend to the mortal world might have an easier time finding a willing teacher in the Host of Heaven should they adhere to a philosophy, but it is certainly possible to get teachings without doing so.
Oriseti Mirei: The Philosophy of Light Alone
The Most Foul is dead in body but alive in spirit, tempting and corrupting mortals. Only by purity of action may one ward off the Most Foul's influence. To exercise pure thought is to eliminate those things which cause corruption, greed, lust, rage, jealousy, egotism, and laziness. To be truly righteous, you must help others to avoid these influences in themselves as well.
Calithra Mirei: The Philosophy of Light and Fire
The world is corrupt; the righteous path is one of moderation. Only by moderation may you mitigate the influence of worldly corruption. You fight the corruption by enjoying the simple pleasures in creation. Causing unnecessary pain, allowing fear to command you: these are manifestations of corruption in the world.
Tharamonian Mirei: The Philosophy of Light and Ice
The world is not corrupt; individual emotions are. The Most Foul was truly destroyed, but the corruption manifesting in the world persists in the emotions and passions of mortals. By not allowing your emotions to rule you, by understanding nature, and by seeking truth, one may walk a righteous path. No nation or king should hold sway over a righteous being.
Kaiomai Mirei: The Philosophy of Fire and Storm
Sometimes destruction is needed, and it is within the created purpose of these celestials to bring that destruction. They are the hand of wrath. Destruction is not, in and of itself, wicked. If something is faced with destruction and survives, then it is made stronger and more pure. It becomes strengthened by the trials it has undergone, and emerges as a tempered instrument. If it is destroyed and wiped away, then it is something that needed to be destroyed, as its entire being was made corrupt and impure by the nature of the physical world. Much like steel, those objects which have many impurities are weaker than those with fewer impurities. It is only by destruction that the strong may be revealed.
Koukla Mirei: The Philosophy of Shadow and Ice
The Koukla Mirei believe that Free will is an illusion. All people are manipulated by things of the world around them to make their choices. For the greater good you may sometimes need to remove this illusion from them. Do not do so without need. It is part of the ineffable plan that this illusion remain in place, to dispel it is a thing that must only occur for the best of causes. If one must remove the illusion, one ought do so with another illusion, or through control. The marks of such methods are easier to remove those of physical damage. The illusion of Free Will is considered the first and most precious comfort to those who must live in the corrupt world.
Liathi Mirei: The Philosophy of Shadow and Storm
Death is the natural end to all life. It gives life meaning by giving it boundaries. Sometimes that means a righteous being must end a life. It is not done lightly, but for just and righteous cause. It is a holy duty, done as a mercy and a kindness. To kill out of anger, revenge, or for petty reasons is the highest of corruptions.