A cult is a heavily corrupt religion of a small size.
All Religions then fall on a spectrum of corruption. They range from heavily corrupt (examples include the medieval catholic church, Islamic extremism, televangelists, and Scientology) to a pure faith (scholarly Islam, some Christian groups, ect.). A corrupt religion is after wealth and power while a pure faith honestly believes and follows what they preach even within the leadership. In most cases if everyone held and practiced a pure faith then most of the problems we experience in our world would be gone.
In case your wondering a pure faith (or at least something that's more toward that end of the spectrum) is called "nondenominational" on a small scale.
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The improbable goal: Fear nothing, hate nothing, and let nothing anger you.