14 Yet perchance inasmuch as He says, My firstborn Son Israel, some one will interpret the fact that He said, My firstborn, so as to deprive the Son of the characteristic property of birth; as though, because God also applied to Israel the epithet Mine, the adoption of those who have been made sons was misrepresented as though it were an actual birth, and therefore the phrase used of Him, This is My beloved Son, is not solely applicable to the birth of God, since the epithet My is (so it is asserted) shared with those who clearly were not born sons. But that they were not really born, although they are said to have been born, is shown even from that passage where it is said, A people which shall be born, whom the Lord has made.
Source: On the Trinity (New Advent)