To start things off, I'm going to post the dictionary.com definition of the word Explain.
"to assign a meaning to; interpret."
Having Explain as Facet #1 is pretty significant as it lends itself to a wide range of uses in the classroom. When teaching, every educator ultimately wants their students to walk away from a class understanding whatever our courses key concepts are. I don't think we can kid ourselves into thinking that our students are going to remember everything we teach them. It's more realistic to try and aim for our students to embody the Six Facets.
Now let's say we were studying a text like Animal Farm by George Orwell. Those of us familiar with the text know that it touches on a variety of issues centered around the Soviet version of Communism. In teaching this text, we would have to draw on a number of historical sources to place its themes and characters within the appropriate context. Ideally, we'd want our students to be able to fully explain the dichotomous nature of the Cold War and how that helped form the thematic underpinnings of the book. However, I'd argue that it would be both more realistic and productive if we focused on imparting on them a few key concepts they can understand, remember, and explain.
For example, it is widely acknowledged that Napoleon's eventual corruption is a key example of how broadly power corrupts and how specifically Stalinistic Communism has strayed from it's egalitarian roots. With both concepts being key themes of the text, I would want my students to be able to express their understanding of these two points more so than actually remembering the full text. If they explain these themes in terms of their relationship to situations and experiences they are personally familiar with either through oral or written assignments, then it is safe to say that your students have successfully mastered the first facet.