conversion

Religious conversion is the adoption of a set of beliefs identified with one particular religious denomination to the exclusion of others. Thus "religious conversion" would describe the abandoning of adherence to one denomination and affiliating with another. This might be from one to another denomination within the same religion, for example, from Protestant Christianity to Roman Catholicism or from Shi'a Islam to Sunni Islam. In some cases, religious conversion "marks a transformation of religious identity and is symbolized by special rituals".
People convert to a different religion for various reasons, including active conversion by free choice due to a change in beliefs, secondary conversion, deathbed conversion, conversion for convenience, marital conversion, and forced conversion.
Proselytism is the act of attempting to convert by persuasion another individual from a different religion or belief system. Apostate is a term used by members of a religion or denomination to refer to someone who has left that religion or denomination.

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