I may have gone overboard...
The Prophet, the Psychopomp, and the Custodian
In the beginning, there were three celestial bodies: the sun, the moon, and the world. They were vain and desired children to admire them. The nature of the sun was fire and so the sun said, "Though I will love and cherish my children, I cannot house them for they will perish in my flames." The nature of the moon was solitude, and so the moon said, "Though I will guide and teach my children, I cannot house them, for they will perish in the cold of the night." The world smiled and said, "I will house all our children, for my nature is to protect. I will clothe, shelter, and feed them." And so it came to be that all the celestial's children lived and died on the world.
As time passed, the moon saw that the children, though happy and healthy, were ignorant. So the moon appointed one among them as her archmage, her prophet, to whom she gifted knowledge and foresight. As the moon reflected light from the sun to illuminate the night, the archmage reflected on the natural world and became wise. He taught the people magic, augury, and reason.
The sun saw that as the children grew wise under the tutalage of the archmage of the moon they began to understand and fear their mortality. Though healthy and wise, they were depressed. So the sun appointed one among them as his archmage, his pyschopomp, to whom she gifted power of death. As the morning sun burns away the nightmares of the night, the psychopomp guided the children through death and sometimes beyond. She taught the people medicine, necromancy, and the observing of death rites.
The world saw up close that some of the children become both wise and powerful under the tutalage of the prophet and the psychopomp. However, although there were great scholars and powerful priests, the world was unfair. So the world appointed one among them as her archmage, a custodian to protect the children who were not as wise or as powerful. As the world shelters the children from the elements, the custodian protected them from cruelty. He taught the people justice, civility, and honor.
Now the three Archmagi push and pull against each other, as the sun, moon, and world push and pull, if any one should become too strong, the other two must pull them back into balance.