Follow this link to read Scamman's Defense of the Christmas Vigil replacing Advent 4 over at the Lutheran Missal blog The gist is this: when December 24th falls on a Sunday, instead of observing the normal Advent 4 readings, the vigil can be observed. It is still Advent. You sing the same hymns. The color is violet. But the readings are different than Advent 4. This only happens about once a decade. I have done it a couple of times and find it very useful. Moving from the vigil on Sunday morning to the Midnight propers in the evening and then Christmas Day for the 25th has a very nice logic to it. By the way, the work that they are doing at the Lutheran Missal Project is very interesting. They aren’t finished yet, but you can sign up to benefit from the work already by being a field tester.