Question: If Christ was born, how could He be eternal and how can He be God? Didn't He have a specific beginning?
The Christian understanding of the “chronology” of Jesus Christ is that He existed as the Son of God eternally, before being born humanly. I emphasize chronology because the word “eternal” indicates that timelines as we see them do not apply to God. There is no beginning, or end of His existance.
Much of what we know of Christ as an eternal being starts from the Gospel of John, chapter 1. In verse 14 of that chapter (I will quote from the New International Version of the bible), John relates the revelation of Christ as God — “The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the One and Only, who came from the Father, full of grace and truth.” This statement shows that the Word became flesh – not like flesh. Jesus was a man.
We can’t fully appreciate this verse without considering verses 1 and 2 of the same chapter — “In the beginning was the Word, and the Word was with God, and the Word was God. He was with God in the beginning.”
He was one with the Father from all eternity. He became Man, taking on a human body. He “was with God” (vs. 1); He “became flesh” (vs. 14). He “was with God in the beginning” (vs. 1); He “made his dwelling among us” (vs. 14). From the eternal position of Godhood to the mortal limitations of manhood!
Paul gives another insight on this in his letter to the Galatians in chapter 4 and verses 4 and 5 — “But when the time had fully come, God sent his Son, born of a woman, born under law, to redeem those under law, that we might receive the full rights of sons.” In these verses Paul establishes the fact that “God sent His Son, born of a woman.”
God sending His Son indicates that God had a Son. Christ was the Son in His eternal relationship with the Father, not because He was born of Mary. Since a son shares the nature of his father, so Christ shares the Godhead, equally with His Father. The Son existed in eternity past before we knew Him. His human birth was merely the method of coming to us.