The answer is in this sentence.
this sentence the letters all exist in "this sentence"
The answer will be 4 letters, then 2 letters.
Essence is spelled with 4 unique letters, and within the word exists "es" and "en"
Add none together.
An essence is something that is a concentration.
Section one, section two.
This part I think means the title and the body of the question given below's "and first section (Mssig Pzle)" statement. U Zin (missing letters of title) in dutch means you sense or you sentence. Although "you sentence" or "sense you" in of itself doesn't mean much In that respect it could indicate an analogy between the puzzles answer if I consider it to be that the title is the "essence" of the entire puzzle itself.
Two per word.
Again, this one might be a bit of a stretch. Missing and Puzzle each are missing 2 letters from each word. In and Uz. In Romanian Uz in mean in household, where as uz by itself means to (all from Google translate). Could be considered "In house" or I interpret it as "inside". Again, this is a weak explanation and how do I relate it to "essence"? Only that the essence of something is usually a building block (house) within (inside) of something else.
Title says it all; no articles and first section (Mssig Pzle)
See above 2 very tenuous explanations.
In ache, in envy
Essences (particularly herbal) are used to sooth all sorts of aches and ailments. Envy I'm lost on honestly..
Probably wrong, but the best I can come up with.