13 And we indeed are sons of God, but sons because the Son has made us such. For we were once sons of wrath, but have been made sons of God through the Spirit of adoption, and have earned that title by favour, not by right of birth. And since everything that is made, before it was made, was not, so we, although we were not sons, have been made what we are. For formerly we were not sons: but after we have earned the name we are such. Moreover, we have not been born, but made; not begotten, but purchased. For God purchased a people for Himself, and by this act begot them. But we never learn that God begot sons in the strict sense of the term. For He does not say, “I have begotten and brought up My sons,” but only, I have begotten and brought up sons.
Source: On the Trinity (New Advent)