14 We believe then In the Only-Begotten Son of God, Who Was Begotten of the Father Very God. For the True God begets not a false god, as we have said, nor did He deliberate and afterwards beget; but He begot eternally, and much more swiftly than our words or thoughts: for we speaking in time, consume time; but in the case of the Divine Power, the generation is timeless. And as I have often said, He did not bring forth the Son from non-existence into being, nor take the non-existent into sonship: but the Father, being Eternal, eternally and ineffably begot One Only Son, who has no brother. Nor are there two first principles; but the Father is the head of the Son; the beginning is One. For the Father begot the Son Very God, called Emmanuel; and Emmanuel being interpreted is, God with us.
Source: Catechetical Lectures (New Advent)