Is it okay to repeat core findings of a cited work in detail? Excuse me for keeping things abstract, I do not want to include more details than necessary.

I'm working on an internship. The internship goal is applying known (published) information and evaluating it in practice. I will conclude the internship by writing a report.

I want to include as much information as necessary in my report for it to be as comprehensive as possible for the reader. This allows the reader to decide if they can skip ahead (instead of me). I do not want to leave details out that may be critical for the readers understanding, even though they seem almost trivial to me, as that makes the report harder to read.

That said, my question:

Is it good form to repeat the core content of the original work in my report, or should I keep it as brief as possible? Is there an accepted middle-ground, or is it not that important as I think? 

Of course I will not literally copy-paste content. I will cite the original work and explain exactly what my contribution is(n't), and refer to the original publication.

My fear is that it seems indecent to "copy" findings that someone spend a lot of effort on.
When you say "core content" I'm assuming you mean the conclusions and, perhaps, something of the methodology. The "findings" of the work. 

If you properly cite the other work, you aren't copying it. You can quote it or paraphrase it accurately, so long as it is cited. But your basic inclination to be complete in this case seems correct. This is especially true if you need to interpret (and justify the interpretation) of the other work(s) in any way. If your readers need to make their own interpretations, things might be more confusing to them as well as being painful to have to find and read the other papers. 

I'm assuming, of course, that a reader of your work won't need to actually completely digest the works on which you base  yours.