Advent marks the start of the Christian year. It is the four weeks before Christmas, This is the Church's New Year's Day. During Advent no flowers decorate churches, but it is usual to have an Advent Wreath.
The word Advent originates from a Latin word “Adventus” which means “coming” or “arrival.” Advent Season is focused on preparing for the coming of Jesus Christ in all ways, from His birth in the past to His Second Coming in the future as the Messiah. For Catholics, Advent is a meaningful season that reminds us of the reality of Jesus Christ and that He has come and He is present in our world and lives. The birth of Jesus is worth celebrating because it reveals His human side and is therefore an example of how we should live our own lives as his followers here on earth.
Advent symbolizes the present situation of the church in these “last days” (Acts 2:17, Hebrews 1:2), as God’s people wait for the return of Christ in glory to consummate his eternal kingdom. The church is in a similar situation to Israel at the end of the Old Testament: in exile, waiting and hoping in prayerful expectation for the coming of the Messiah. In the same way, the church, during Advent, looks back upon Christ’s coming in celebration while at the same time looking forward in eager anticipation to the coming of Christ’s kingdom when he returns for his people.
In this light, the Advent hymn “O Come, O Come, Emmanuel” perfectly represents the church’s cry during the Advent season. While Israel would have sung the song in expectation of Christ’s first coming, the church now sings the song in commemoration of that first coming and in expectation of the second coming in the future.