Show, don't tell
Writers read the story many times and are inherently omniscient on subsequent reads, readers will react to omniscience with boredom or confusion because being told by an all-knowing omniscient narrator or dialogue is dull and breaking the 4th wall.
I hated hearing this repeated "advice".
My post below will instead focus on omniscience being the storyteller, the tell part that many writers ignore or forget, but every reader feels jarring and unrealistic.
Writers read the story many times and are inherently omniscient on subsequent reads, readers will react to omniscience with boredom or confusion because being told by an all-knowing omniscient narrator or dialogue is dull and breaking the 4th wall.
Enjoy this basic advice, applied to a timeless writing guideline in a novel way.
It was said to me constantly during my early days writing, and no one ever properly explained the concept in a way that actually made sense to me. Until I did a creative writing course, with an amazing teacher. She started talking about the omniscient narrator
How it tells the reader what's going on.
And when I heard her start to say this I thought to myself HERE WE GO AGAIN But she said the narrator is extremely important, so I kept an open mind as this was already describing something new to me.
When writers use their omniscient voice it is almost always not using a perspective.
The omniscient narrator is usually jarring to readers, because the lack of perspective. Being omniscient inherently means all-knowing, so if the book is in 1st, 2nd, or 3rd person perspective they suddenly can see or know things that they couldn't possibly know.
That's when the author is narrating, not the character, not the story narrator that is true to the current perspective.
Omniscient is a 4th kind of perspective.
Heard about the "4th wall"? It's when the character, not the author, breaks the perspective and speaks directly to the reader.
This is when the writer embraces the Omniscient 4th person perspective.
This, and omniscience, are commonly mixed up with the writing technique known as POV (point-of-view) - but are distinct concepts.
Perspoctive is determined by how the dialogue AND narrator usewords to reference themselves as "I" "my" "mine" for 1st person. 2nd person uses "you" "your" "yours", and third person perspective is the most common that names characters by name and describes them using "he" "she" "they" "them".
POV is when a chapter focuses the story on a character, from their own viewpoint, regardless of the perspective being used.
This concept of perspective needs to be mastered by all authors, and a lot of author's can release many books and still get it wrong, assuming perspective and POV are the same thing.
Some full examples of perspectives are:
1st person dialogue should also narrate using; I felt, I went, I smelled. 2nd person dialogue says; you are, you felt. And even when narrating it should be written as; you go to, you think about. 3rd person perspective can have a few descriptions, I was taught that as long as it uses character names and will not write like 1st or 2nd person perspectives, then it's 3rd person. This is why it is the most common, it is the easiest perspective for new authors because it is how most people write when they are not trying to be a professional writer. So beware the omniscient narrator in 3rd person!
Try to still keep the perspective
If the POV character of your chapter is in 3rd person for dialogue, ensure the narrating stays consistent as 3rd person also. And do not narrate things the character is unable to know!
That's the secret to; show, don't tell