This year Advent is a short 3 weeks. It's a wonderful season that always goes by too fast.
Advent is divided into two parts. The first lasts until December 16, and the second is from Dec. 17 to 24.
The second part is the immediate preparation for Christmas and focuses more intensely on the Scripture prophecies about the coming Messiah.
Advent is all about waiting. In general, we are awaiting Christ's coming. We look forward to his final coming in glory, so the liturgy highlights this in certain ways. For the past two weeks we've already been reading the Book of Revelation at Mass. It provides a good transition into our Advent expectations.
But there is also a more immediate coming of Christ by grace into our hearts. Although he's already with us, grace can fill us more and more in different ways. So we pray for an abundance of grace as we prepare to celebrate his birth.