Cyril of Alexandria Identifies The Baptized as 'Firstborn Sons'

Moreover, if the first are confessedly the cause of the second, but God and the Son of God are first, then the Son is the cause of those who have the name of sons, inasmuch as it is through Him that they have obtained the appellation. He, therefore, who is the cause of the second sons may justly be called the Firstborn, not as being the first of them, but as the first cause of their receiving the title of sonship. [Cyril of Alexandria, Homily 1 on Luke 2.4-8]