Where is the subject and verb here etc.?

The sentence "The principle is, the farther from the scene of horror, the easier the talk." looks and sounds fine to me, but if I wrote it my internal editor would worry vaguely. To make things less vague here are some questions:

Is "the principle" the subject?

Is "is" the verb?

Are the phrases "the farther[...]" and "the easier[...]" adverb phrases or prepositional phrases or something else?

Yes, "the principle" is the subject of the verb "is". The complement is the phrase following the first comma.

Here's a question which describes that construct: "the comparative, the comparative" vs. "as-clause"

The statement would be clearer if the principle were to be enclosed in quotes or denoted in some other way, for example by a colon:

The principle is "the farther from the scene of horror, the easier the talk"
The principle is: the farther from the scene of horror, the easier the talk.