“God is eternal and without beginning. But Jesus was born in Bethlehem of Mary. Therefore, Jesus cannot be God, since he has a beginning.”
This argument confuses two levels. The birth of Jesus in Bethlehem concerns his becoming human, not his eternal origin. The faith of the Church clearly professes: Jesus Christ, as God, has been with the Father from all eternity—“In the beginning was the Word, and the Word was with God, and the Word was God” (John 1:1). The Son has no beginning; he is “begotten of the Father before all ages” (Nicene Creed). However, in time he assumed a human nature and was “born of the Virgin Mary” (Gal 4:4).
The birth in Bethlehem therefore concerns his humanity, not his divinity. As Athanasius says: “It is the same one who is begotten of the Father before all ages and who in the last days was born of Mary for us” (Orationes contra Arianos II,70). Augustine explains: “Before time he was born of the Father, in time of the mother” (Sermo 186,1).
Scripture itself distinguishes: “His origin is from of old, from ancient days” (Mic 5:2). Jesus declares: “Before Abraham was, I am” (John 8:58)—he does not say “I was,” but “I am,” thus claiming the divine name from Ex 3:14.
The Incarnation is therefore not a limitation of eternity, but its revelation: The eternal God enters time without losing his eternity. Whoever confuses the birth in Bethlehem with a “beginning of God” fails to recognize the difference between nature and person: A divine person assumes a human nature.
Counterargument from the Other Side
“But a birth always means a beginning—so Jesus cannot be eternal.”
Brief Refutation
The birth in Bethlehem concerns his humanity. In his divinity, he is eternally “begotten, not made.” Two different births, one and the same Lord: eternally from the Father, temporally from Mary.