"Rage, rage against the dying of the light."

• Dylan Thomas
  

I think this film is under-rated. Sure, it's a little preachy in a way that folks are not used to.
And, the flash-backs, PTSD and dementia-like moments sometimes intertwine and make it harder to follow. And, few people play "crazy" as manically as Cage, but too much crazy can get in the way of story telling too.

The title can suggest - not surrendering; not giving up; fighting for your "values" to the bitter end.
A second meaning that works for me, is that we may - in these troubling times - be witnessing "the dying of the light" of that "shining city on the hill" that Reagan referred to.

Cage plays an old-school (very old-school) "patriot" who has devoted his life (beginning in the Marine Corps) to defending his country.

But, I suppose the "higher ups" don't value what he represents. And, the top-heavy CIA bureaucrats have lost touch with their "values"; turned into political lackeys.

Cage's character rages about the CIA's failures to do the right thing; to keep America safe. He points out that the CIA does not have the courage of it's convictions to stand up to Presidents when they are wrong; to report the inconvenient truths.

Examples of our intelligence community failures; a few of the many: Most now understand that 9/11 happened because of a massive intel failure and failures to act pre-emptively. And, when we withdrew the bulk of our forces from Iraq - our intel folks warned the President's office of the threat of forces coming down from Syria, but those were ignored. And, Afghanistan? The previous administration set up steps for an orderly withdrawal. Our intel folks saw those steps were being broken early on when we could have slowed their advance and gotten our gear, our selves and allies out of there in an orderly fashion. But our CIA leadership has been neutered into becoming "yes men".

So yeah, Cage's character is mad as hell at what has happened to his CIA; broken; losing sight of it's values.

Dying of the Light had important messages to convey, but those messages flickered in a liberal-dominated Hollywood.