The Church is called Catholic or universal because it has spread throughout the entire world, from one end of the earth to the other. Again, it is called Catholic because it teaches fully and unfailingly all the doctrines which out to be brought to the people’s knowledge, whether concerned with visible or invisible things, with realities of heaven or the thing of earth.

It is most aptly called a church, which means an “assembly of those called out [i.e., holy],” because it “calls out” all people and gathers them together, just as the Lord says in Leviticus: “Assemble all the congregation at the door of the tent of meeting.” It is worth noting also that the word “assemble” is used for the first time in the Scriptures at this moment when the Lord appoints Aaron high priest. So in Deuteronomy God says to Moses: “Assemble the people before me and let them hear my words, so that they may learn to fear me.” The churches of Christ are already multiplying throughout the world, and of them it is said in the psalms: “Sing a new song to the Lord, let his praise be sung in the assembly  of the saints.”

—Cyril, Bishop of Jerusalem (late 4th century), Catechesis 18.23