The word Trinity describes the belief in Christian theology that the one God of the universe is comprised of three persons: the Father, the Son, Jesus Christ, and the Holy Spirit. It has been the conviction of Christians throughout the centuries that this is what the Bible teaches. The word "trinity" comes from the Latin word trinitas, meaning "three." (Learn more about the Father here, Jesus Christ here, and the Holy Spirit here.)
The word trinity doesn't appear in the Bible; it is a theological label meant to summarize the teachings of certain passages of Scripture. (Other important theological terms that don't appear in Scripture, but many Christians believe are taught in it, include "communion," "incarnation," "free will," "rapture," and "advent.") The early church father Tertullian (c. 155-230), who wrote in Latin, is believed to have first used the term trinity to describe the God of the Bible. (Learn more about Tertullian here.)
The doctrine of the Trinity distinguishes Christianity from other religions including, Mormonism, Jehovah's Witnesses, and Unitarian Universalism. These groups reject the doctrine, in part, because the word trinity isn't used in the Bible, it doesn't make philosophical sense to them, and they don't believe that it's compatible with monotheism. (Learn more about Mormonism here, Jehovah's Witnesses here, and Unitarian Universalism here.)
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