According to the legend, because the son of god was born.
Two Christmas carols that mention angels are "Hark! The Herald Angels Sing" and "Angels We Have Heard on High." Both songs celebrate the role of angels in announcing the birth of Jesus.
Jesus - IS - God. That's the whole concept of Christianity in three words. So, the angels cannot sing to God without singing to Jesus.
shepherds
They were first fearful of them, but the angels told them to not fear them because Jesus had been born
It was the angels who announced it to the shepherds.
The angels told them.
The angels sang to the shepherds about the birth of Jesus, proclaiming peace and goodwill. They announced that a Savior, Christ the Lord, had been born in Bethlehem, bringing joy to all people. This heavenly message emphasized the significance of Jesus' birth and the hope He would bring to humanity. The shepherds were filled with awe and excitement at this celestial revelation.
Angels were gods messengers, and they told the word of the birth of Jesus to humble shepards.
the birth of jesus
When the Angels Sing was created in 2000.
Mary, then Joseph, then Mary's cousin, Elizabeth.
The angels delivered a message of joy and peace, announcing the birth of Jesus Christ and proclaiming that he was the Savior and Messiah.