The last Sunday of Ordinary Time is set aside as a feastday called Christ the King. This year it falls on November 20. It's a day when Christians recall that we are part of a different Kingdom and serve a different King, that Christ came to reign in our lives and in the world. In the upside-down Kingdom of God, we manifest the kingship of Christ through humility, service, and sacrificial love.
The Feast of Christ the King then gives way to the First Sunday of Advent, when we long for Christ to come with expectancy and ache.
In this way, the end and new beginning of the Church Year is a kind of paradox. We move from coronation to expectation. We celebrate Christ's kingship over all things, then we ache for His return, knowing that we still await His full reign, the full restoration of the created order, the complete repair of all that's broken.