The Catholic, or universal, Church gets her name from the fact that she is scattered through the whole world from the one end of the earth to the other, and also because she teaches universally and without omission all the doctrines which are to be made known to mankind, whether concerned with visible or invisible things, with heavenly or earthly things. Then again because she teaches one way of worship to all men, nobles or commoners, learned or simple; finally because she universally cures and heals every sort of sin which is committed by soul and body. Moreover there is in her every kind of virtue in words and deeds and spiritual gifts of every sort. The Church, that is, the assembly, is designated by this apt term, because it assembles all and brings them together, as the Lord says in Leviticus: Assemble all the congregation at the door of the tent of meeting. Moreover it is worth noting that this word ‘assemble’ is first used in scripture in the place where the Lord appointed Aaron to the high priesthood. And in Deuteronomy God says to Moses: Assemble the people that they may hear my words, that they may learn to fear me. He mentions the Church or assembly again when he speaks of the tables of the law. In them were written all the words which the Lord spoke with you on the mountain, out of the midst of the fire, on the day of the Church or assembly – or to put it more clearly, On the day on which you were called by the Lord and assembled together. The psalmist also says: I will give you thanks, O Lord, in the great Church, in the gathering of the throng I will praise you. Earlier the psalmist had sung: Bless the Lord in the Church, bless God, you who are Israel’s sons. The second Church the Saviour built from the Gentiles, our holy Church of the Christians, of which he said to Peter: On this rock I will build my Church, and the powers of death shall not prevail against it.
After the particular Church of Judea was repudiated, many Churches of Christ are now multiplied throughout the whole world, of which it is written in the psalms: Sing to the Lord a new song, let his praise be in the Church of the saints. Echoing this the prophet said to the Jews: I have no pleasure in you, says the Lord of Hosts and immediately adds, For from the rising of the sun to its setting my name is great among the nations. About the same holy Catholic Church Paul writes to Timothy: That you may know how one ought to live in the household of God, which is the Church of the living God, the pillar and bulwark of the truth.
-- From the Instructions to Catechumens by St Cyril of Jerusalem
(Taken from today's Office of Readings, via Universalis)