From Catechetical Lectures, XVIII (NPNF-II, Vol. VII):
But since the word Ecclesia is applied to different things (as also it is written of the multitude in the theater of the Ephesians, And when he had thus spoken, he dismissed the Assembly), and since one might properly and truly say that there is a Church of evil doers, I mean the meetings of the heretics, the Marcionists and Manichees, and the rest, for this cause the Faith has securely delivered to you now the Article, “And in one Holy Catholic Church;” that you may avoid their wretched meetings, and ever abide with the Holy Church Catholic in which you were regenerated. And if ever you are sojourning in cities, inquire not simply where the Lord’s House is (for the other sects of the profane also attempt to call their own dens houses of the Lord), nor merely where the church is, but where is the Catholic Church. For this is the peculiar name of this Holy Church, the mother of us all, which is the spouse of our Lord Jesus Christ, the Only-begotten Son of God (for it is written, As Christ also loved the Church and gave Himself for it, and all the rest,) and is a figure and copy of Jerusalem which is above, which is free, and the mother of us all; which before was barren, but now has many children.
…In this Holy Catholic Church receiving instruction and behaving ourselves virtuously, we shall attain the kingdom of heaven, and inherit ETERNAL LIFE.