We celebrate the miracle of the incarnation at Christmas as we will for eternity. The second person of the Trinity took on flesh, really and truly, and did not throw away or alter His divinity. He remains the Word of God and ever since His conception by the Holy Spirit in Mary is also a true man - "true man yet very God" as the hymn says. Keeping these together in our heads, hearts, and lives is the glory of Chalcedon, the Definition we confess as Christmas about the Lord Jesus Christ.