1 As it has been clearly demonstrated that the Word, who existed in the beginning with God, by whom all things were made, who was also always present with mankind, was in these last days, according to the time appointed by the Father, united to His own workmanship, inasmuch as He became a man liable to suffering, [it follows] that every objection is set aside of those who say, “If our Lord was born at that time, Christ had therefore no previous existence.” For I have shown that the Son of God did not then begin to exist, being with the Father from the beginning; but when He became incarnate, and was made man, He commenced afresh the long line of human beings, and furnished us, in a brief, comprehensive manner, with salvation; so that what we had lost in Adam— namely, to be according to the image and likeness of God— that we might recover in Christ Jesus.
Source: Adversus haereses (New Advent)