For many people, motion pictures are not "just" an entertainment medium. Instead, they are not unlike any other form of artistic expression, filled with the realities (good or bad, perceived or real) of the time period in which they were made. In essence, films can be considered to be kind of a "time capsule" for the human condition, told in the form of scripted tales. As such, many such works of art deserved to be saved, which is exactly what this documentary focuses on.
For a basic plot summary, "These Shadows" describes how certain films (voted on by a panel of motion picture luminaries) are currently being preserved in the Library of Congress (or our "national library") for future posterity. However, problems often exist in restoring the original negatives of even such classic pictures as "Gone With The Wind" or "The Wizard of Oz".
"These Shadows" takes very much of a "big picture" look at film preservation. While it could have spent hours on the fascinating topic of the physical restoration process itself, the filmmakers instead give an overview of the entire Library of Congress process, from its beginning (aka finding the funding) to which movies are selected and finally to how the overall scheme of things will proceed into the future. Any one of these areas could have been focused on in their own documentaries, but here they are condensed into the overall narrative of the project.
Overall, then, this is a fun little documentary that introduces us to the very concept of preserving motion pictures as we would other works of art or historic culture. Anyone who enjoys the film arts will likely agree that its place in our own national culture is very deserving.