What's the difference between Arc Words and Meaningful Echo?

I'm aware that a repeated line in a film does not cover the overarching message of the film. But how do you know when it's just repeated, or when it's integral to what's going on? I may also be nudging myself towards Foreshadowing, so what definitions are there to untangle myself from these terms?

I've also figured out some crucial lines of dialogue in the film Equilibrium.

"It's my job to know what you're thinking." "I pay it gladly." "I told you I'd make my career with you." Paraphrased: "You're treading on my dreams."

There's a variant in who echoes the dialogue, but I'm not sure if this adds to the overarching theme, or if it just gets meaningfully echoed by another character. Is there any meaning to who echoes it - either the same person or someone else?

Courtesy links: Arc Words and Meaningful Echo.

In short, Arc Words is when the phrase is repeated throughout the work, while Meaningful Echo is where something that was once said is repeated in a meaningful manner to reflect the particular scene where it was said the first time, perhaps to highlight the change that's gone on between.

Arc Words is (or can be) a type of Foreshadowing. A Meaningful Echo isn't.

edited 19th May '14 2:30:22 PM by AnotherDuck

Arc Words is something repeatedly said as part of the Central Theme, like a spy flick and "Trust no one." A Meaningful Echo can overlap with arc words but is typically only repeated once with any number of reasons why, not specifically tied to the theme of the plot.