a Theological Caste System, or Cast System depending on the planetary translation, is a planet that uses religion to determine value. In many cases, it also includes civilizations where religion is determined by parental belief, rather than personal belief. It is a matter of perspective as to wether this helps or hinders a civilization. There are many examples of this including:
(see Religions Of Earth)
Though not a theocracy, religion is determined by the parents religion (conversion is allowed however). Many governments on Earth however, persecute people of different religion, or use it to control the population. Earth is unique in that whenever a religion is proven to be wrong, improbable, or contrary evidence is presented, the majority still choose to hold it as the "Gospel Truth" (no pun intended) rather than presenting new theory, more accurate ideals, or adjusting to social climate. In fact many will make up odd irrational sounding excuses as to why its still true (ie "God placed dino bones on earth to confuse people for no good reason", "The moon landing was staged", or even outright condemning the discoverers of new data). It also is established in a way that prevents the creations of new religion via individual hypothesis (ie one cannot create their own religion and have it be taken seriously). This sort of theological filter has halted the production of new religious theory, and kept a repeating cycle of the two most popular religions (Christianity, and Islam) in motion constantly jockeying for position of control. This has calmed down in recent times, as many people now see God as a kinder accepting being, that created everyone for a purpose, rather than for entertainment, war, or superiority. However, creating your own religion does not allow it any legal status in most nations, causing many to choose from pre rendered religions rather than form unique theories. Again wether or not this is beneficial is a matter of opinion.
Zayke has been a victim of religious theological casting as well, as it has a single (however broad) prevailing religion known as Karyana (car EE anne UH). Detractors are not persecuted and have not been since the "Blind Age", however there is a small filter on the creation of new theology, because society is structured in a way somewhat based on Karyana teachings (ie one must apologize for killing game, one must live by certain principles such as the Best as You Can Be principle, etc). These are considered integral parts of social structure on Zayke but one can opt out, and live a different lifestyle, without persecution (except in the Jakid lands, where you at least have to contribute to community in order to live there). Karkans accept all other religions from any planet regardless of how inane they consider it, because part of their code is to live and let live. In their Dark Age, they attempted to colonize their cluster, and spread the religion, leaving to this day, practicers of Karyana on a far spread amount of planets, including Zeta Reticulon 9.
On Mars in ancient times, the religion Bok Tu'lara was enforced strictly. Society was theological to a fault, and detractors were killed. After a massive war, they decided to ban theology, an act in which itself can be considered theological control, because it filtered out all religions whatsoever from being created. When their atmoshpere broke down and the oceans disappeared, the few remaining Martians dumped all aspects of their culture as a "failed existance" and formed a provisional government that welcomed mixed ideas from any incoming species wanting to settle there. Today they gladly allow Human, Karkan, and Grey culture to form an eclectic mix in their new world.