There are two traditions for the theme of the Last Sunday of the Church Year.
The older tradition is the emphasis of End Time and its transition into Advent. In the Historic Lutheran Lectionary, the Gospel for the Last Sunday of the Church Year was the parable of the ten virgins, with the emphasis on readiness for Christ’s return. Sometimes this was called “Sunday of the Fulfillment.” (See Wikipedia article on Totensonntag, and two articles (1, 2) on “Sunday of the Fulfillment” from www.higherthings.org.)
The newer tradition is the observance of Christ the King, which is also fitting. Christ is the Alpha and the Omega, the beginning and end of all things. Often Christ the King has a passion emphasis, which shows us that Christ as King is not always what we would expect. The passion Gospels are an opportunity to proclaim the Theology of the Cross. Even as King, Christ suffered, and he revealed the glory of his love in his suffering. As his loyal subjects, we can expect suffering in the world, too.