When the language in a work of literature such as "Beowulf" is difficult to understand, it is helpful to read from an edition that includes a commentary — an explanation or expansion or criticism added to the original material.
Editorials go hand-in-hand with commentaries, since both express a writer's opinions. Commentary can be oral as well as written. Each year, following the President's State of the Union address, you can tune into the networks for commentary from respected news anchors. In fact, political commentary has become so pervasive in our media that some feel it has replaced reporting.