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The word catholic literally means "universal," as in "the universal church." It originally was applied to all Christians because we are all part of the universal church in the way that we are all members of the Body of Christ. The Latin word is catholicus, and in Greek it is katholikos, from the Greek phrase meaning "on the whole, according to the whole or in general." The word in English can mean "including a wide variety of things; all-embracing," or "of the Roman Catholic faith," or "relating to the historic doctrine and practice of the Western Church.”
Catholic was first used to describe the Christian Church in the early 2nd century to emphasize its universal scope. The term has been incorporated into the name of the largest Christian communion, the Roman Catholic Church, which consists of 23 churches sui iuris, in full communion with the Bishop of Rome. The largest of these, the Latin Rite consists of nearly 95 percent of the population of the Catholic Church. The remaining 5 percent consist of the 22 Eastern Catholic Churches. Some Protestant churches use the term "catholic Church" to refer broadly to all believers in Jesus Christ across the world and the ages, regardless of denominational affiliation. Generally, to avoid confusion between this concept and the Roman Catholic Church, theologians will refer to the “universal church” as the “church catholic,” utilizing the lower case, instead of “Catholic Church.”
The Eastern Orthodox, Oriental Orthodox, Anglican, and Lutheran, and some Methodists declare that their churches are catholic in the sense that they are in continuity with the original universal church founded by the apostles. The Roman Catholic, Eastern Orthodox, and Oriental Orthodox churches all believe that their church is the only original and universal church. Catholicity is considered one of Four Marks of the Church, the others being unity, sanctity, and apostolicity according to the Nicene Creed of 381: "I believe in one holy catholic and apostolic Church." It is crucially important to remember, though, that when the early Christians used the term “catholic,” they were not referring to any particular church, denomination, rite, or communion. They were simply referring to all true believers in the Lord Jesus Christ.
