Luke 15:10 NKJV - "Likewise, I say to you, there is joy in the presence of the angels of God over one sinner who repents."
From Jesus' birth to a sinner's "new birth," the angels rejoiced. They knew that Jesus could save sinners and they rejoiced when He did. Not only is Christmas a time for song, but every time "Christ is born in the heart of a repentant sinner" we should rejoice with the angels that "a new name is written down in glory!"
Heaven is a place of Joy and Song! You can't read the Book of Revelation without seeing that. And a Christian living a heavenly life on earth should be no less joyful. Remember, the "fruit of the Spirit is love, joy, peace..." Love produces joy and joy makes way for peace. Interesting: God's love is seen in His Gift and when that Gift came to earth the angels were filled with joy and in their joy they sang of "peace on earth..."
May we not keep silent this Christmas. Our Christmas carols still bring a sense of "peace" and remind us that the Prince of Peace is getting ready to bring that peace to earth! Sing and rejoice!