Read this passage from the Bible first:
26 In the sixth month of Elizabeth’s pregnancy, God sent the angel Gabriel to Nazareth, a village in Galilee, 27 to a virgin named Mary. She was engaged to be married to a man named Joseph, a descendant of King David. 28 Gabriel appeared to her and said, “Greetings, favoured woman! The Lord is with you!”
29 Confused and disturbed, Mary tried to think what the angel could mean. 30 “Don’t be afraid, Mary,” the angel told her, “for you have found favor with God! 31 You will conceive and give birth to a son, and you will name him Jesus. 32 He will be very great and will be called the Son of the Most High. The Lord God will give him the throne of his ancestor David. 33 And he will reign over Israel forever; his Kingdom will never end!”
Luke 1: 26-33
Now listen to the Christmas Carol - "O come, O come Emmanuel" below: