In the book of Luke, what is significant about the birth narrative of Jesus?
The most notable difference among the four gospels of the New Testament, Matthew, Mark, Luke, and John, is that there is an introduction to the story of the birth of Jesus in all but the gospel according to Luke. Saint Matthew begins with the history of the "generation of Jesus Christ, the son of David, the son of Abraham." That is, St. Matthew traces the genealogy of Jesus Christ in Chapter I. Saint Mark prefaces his account of the birth of Jesus with a formal introduction,
The beginning of the gospel of Jesus Christ, the Son of God....
He then describes the "messenger" of the Savior, John the Baptist, who introduces Jesus as an adult, who comes from Nazareth.
In a similar fashion, the gospel according to Saint John introduces Jesus as "the Word was made God," and has the adult Jesus preceded by John the Baptist, However, in the gospel according to Saint Luke, he writes to Theophilus, explaining that it seems best to him to record the life of Jesus in chronological order so that there be better understanding and certainty of the truth:
...thou mightest know the certainty of those things, wherein thous hast been introduced.
Thus, St. Luke begins with the appearance of the angel Gabriel, who announces to Mary that she will conceive a child. Then, he describes the birth of Jesus and chronicles His life and teachings.