The Enchiridion

We need not therefore take for granted, that whatever is born of a thing is immediately to be declared the son of that thing. For, to pass over the fact that a son is born of a man in a different sense from that in which a hair or a louse is born of him, neither of these being a son; to pass over this, I say, as too mean an illustration for a subject of so much importance: it is certain that those who are born of water and of the Holy Spirit cannot with propriety be called sons of the water though they are called sons of God the Father, and of the Church their mother. In the same way, then, He who was born of the Holy Spirit is the Son of God the Father, not of the Holy Spirit. For what I have said of the hair and the other things is sufficient to show us that not everything which is born of another can be called the son of that of which it is born, just as it does not follow that all who are called a man's sons were born of him, for some sons are adopted. And some men are called sons of hell, not as being born of hell, but as prepared for it, as the sons of the kingdom are prepared for the kingdom.