Christmas is about the birth of the Gospel in the flesh of Christ. The Gospel is
  confessed in the Apostle's Creed, but obviously, at Christmas there is only a small part
  of the Creed to confess. At the birth of Christ, the shepherds knew even less about the
  Gospel than was known by Mary and Joseph.
  The question here is, when was the Gospel in the New Testament first proclaimed and who
  proclaimed it?
  We know that the Gospel is proclaimed throughout the Old Testament beginning in Genesis
  3:15 as God's promise through the Seed of the woman. The word "Gospel," however,
  comes to us from a Greek word, which means "good news," in this case, good news
  about Christ.
  The word "Gospel" is a noun and "to preach the Gospel" is the verb
  form. According to the UBS notes, the verb form is "euvaggeli,zw" [euaggelidzow]
  which means to bring the good news, preach the good news (sometimes preach the good news
  to, e.g. Acts 8.25); preach, proclaim; passive voice, hear the good news (of persons); be
  preached (of things).
  The first use of the word "Gospel" appears in the New Testament when the
  Angel Gabriel speaks it to Zechariah, who is John the Baptist's father. "And the
  angel answering said unto him, I am Gabriel, that stand in the presence of God; and am
  sent to speak unto thee, and to shew thee these glad tidings." Luke 1:19
  An angel also spoke the Gospel to the Shepherds on the night of Christ's birth.
  "And the angel said unto them, Fear not: for, behold, I bring you good tidings of
  great joy, which shall be to all people." Luke 2:10
  Both of these verses could have been translated, "I preach to you the
  Gospel."
  Of course, the meaning of the Gospel is often expressed without the use of the word
  "Gospel," such as the Gospel spoken by Zechariah after the birth of John when
  Zechariah prophesies that John's work will be "To give knowledge of salvation unto
  his people by the remission of their sins." Luke 1:77
  Gabriel speaks the Gospel to Mary when he says to her about Jesus, "He shall be
  great, and shall be called the Son of the Highest: and the Lord God shall give unto him
  the throne of his father David." Luke 1:32
  Elisabeth spoke the Gospel to Mary when she says, "And blessed is she that
  believed: for there shall be a performance of those things which were told her from the
  Lord." Luke 1:45
  Mary responded with the Gospel to Elisabeth in the "Magnificat" when she says
  about Christ, "He hath holpen his servant Israel, in remembrance of his mercy; As he
  spake to our fathers, to Abraham, and to his seed for ever." Luke 1:54-55
  "Simeon spoke the Gospel to Mary and Joseph in the Temple when he says to the 40
  day old infant Christ, "For mine eyes have seen thy salvation." Luke 2:30
  Anna spoke the Gospel to people in the temple at the same time when she saw the baby
  Jesus, "And she coming in that instant gave thanks likewise unto the Lord, and spake
  of him to all them that looked for redemption in Jerusalem." Luke 2:38
  In all the above examples we should note that the time had not yet come for the Gospel
  about Jesus Christ to be preached to the general public. It took another 30 years until
  John the Baptist would be the first to preach the word "Gospel" in a sermon in
  Luke 3:18 where we read, "And many other things in his exhortation preached he unto
  the people."
  The King James, NIV, and NASB use the words "exhort" or
  "exhortation" where the Greek word for "preach the Good News" or
  "Gospel" is actually used. The Greek word for Gospel is there in the text but
  the average reader will not recognize it. However, Beck and Lenski translate more clearly,
  that John "was telling people the good news" or "continued to preach the
  Gospel."
  But what kind of Gospel did John preach that causes some translators to call it
  "exhortation" instead of "Gospel?" He didn't speak about the
  suffering, crucifixion, death, resurrection and ascension of Christ. Rather, he only
  preached on one phrase about the Gospel as found in the Apostles' Creed "the
  forgiveness of sins."
  We read earlier in the chapter, "And he came into all the country about Jordan,
  preaching the baptism of repentance for the remission of sin."(Luke 3:3) These are
  the same words given to Zechariah above in Luke 1:77.
  We should also note that Zechariah, a priest, was struck dumb by the angel after first
  hearing the "Good News" above in Luke 1:19. According to Luther 's understanding
  of vocation and "the call" Zechariah would have been the only one of the
  examples given above who could have preached the message of the Gospel in public, but his
  doubts were chastened with the inability to speak the Gospel in the temple. This privilege
  would be reserved for his son John, which is why Christ calls John the greatest man that
  ever lived according to Luke 7:28.
  John the Baptist clearly depicts the meaning of the first Gospel when he sees Christ
  and says, "The next day John seeth Jesus coming unto him, and saith, Behold the Lamb
  of God, which taketh away the sin of the world." John 1:29
  Luke ends his Gospel with almost the same message of John the Baptist. Compare these
  verses: "And he [John] came into all the country about Jordan, preaching the baptism
  of repentance for the remission of sins." Luke 3:3
  At the end of Luke Christ says to the disciples, "And that repentance and
  remission of sins should be preached in his name among all nations, beginning at
  Jerusalem." Luke 24:47
  The essential message of the Gospel is the same at Christmas, as Christ says will be
  preached until the end of time.