Originally written in Latin almost 10 centuries earlier, and translated into English during the mid-19th century, O Come, O Come, Emmanuel is a hymn based on prayers, called vespers, that are prayed every day for 7 days before the celebration of Christmas.
I've always loved the reality of living in seasons. Just like the seasons of spring, summer, autumn and winter, there are different seasons in the divine and the human journey, and the highs and lows, the louds and softs that come with each. As with every season, one isn't whole without the season before it. The same is true with Christmas. Christmas isn't Christmas without the season before it, Advent.
The text of O Come, O Come, Emmanuel is based on the biblical prophecy from Isaiah 7:14 that states that God will give Israel a sign that will be called Immanuel, literally meaning "God with us." But there needed to be an arrival of that truth. As well, there needed to be a waiting for God to come to truly appreciate His arrival. Matthew 1:23 states fulfillment of this prophesy in the birth of Jesus of Nazareth.
There is Good News in the reality that Jesus is with us, but there is also Good News in knowing He is coming again. So in that mystery, we can be in a sense of solidarity with those who were waiting for the Messiah to come; and those who, throughout the history of the Church, have been waiting for His return.
Hear 'O Come, O Come, Emmanuel' at TheOverflow.com