[thaumasiotes]

No, it can't be both. "Get this through your skulls" is not an idiomatic† way to say "listen to this" in English. It's an idiomatic way to say "listen to this, idiots". It isn't possible for an expression to be simultaneously unmarked and marked.

For a different Biblical phrase, Jesus is often reported as greeting people with the expression "peace be upon you". This is not exotic; the reason he's doing that is that it's Aramaic for "hello". (And still "hello" today in the region, but we tend to write down the modern version as "salaam" rather than "peace be upon you".)

† It occurs to me, given your question, that you might be confused over the difference between "idiom" [meaning: a more or less fixed expression whose meaning is opaque] and "idiomatic" [meaning: (of a manner of speaking) ordinary / natural / unlikely to raise eyebrows]

It's sense (1) here: https://en.wiktionary.org/wiki/idiomatic ("Pertaining or conforming to [...] the natural mode of expression of a language"), not sense (2).

[gwd]

So I mean, I've only been reading the NT regularly for about 2 years; and in any case the source text itself is 2000 years old, and the quote itself will almost certainly have been a translation from a very different language (Aramaic into Greek). So it's certainly not impossible that those words are just the way you say that in that language.

That said:

- I have learned quite a number of languages at various levels, including French, Turkish, Mandarin, Cantonese, Koine Greek, German, and Japanese. I can have conversations in French and Mandarin, and I'm reading mid-length paragraphs in Koine Greek. So I've been exposed to a fair range of non-English idioms (as in definition 1, "natural mode of expression").

- If there were other examples of this particular idiom in the NT, the study method I use [1] is highly likely to have shown them to me; but I haven't seen other examples of it.

One thing about low-key idioms is that they're short and easy to say; e.g., the idiomatic way to say "quickly" in Mandarin is 马上, which literally means "on a horse". Nobody thinks about horses when they say that; but it's fast enough to go by quickly. When I read the words in Greek out loud, they're not quick -- it's long, and the rhythm of the words slow the phrase down.

Looking at the grammar and the context, in my judgement, I think it very unlikely to be simply be an idiomatic way to say, "Listen carefully"; I go into more detail in a sibling comment:

https://news.ycombinator.com/item?id=43837037

But hey, I could be wrong. :-)

[1] "Guided immersion" https://www.laleolanguage.com