Dialogue, in its most natural state, has the ability to move the plot and show character traits, as well as its most basic function: communication. When I read submissions this often marks the difference between a writer that ‘gets it’ and a writer that has a long way to go.
Dialogue must speak for itself. If you have to set up the dialogue before or explain it after you haven’t written good enough dialogue:
“Imagine you’re at a play. It’s the middle of the first act: you’re really getting involved in the drama they’re acting out. Suddenly the playwright runs out on the stage and yells, ‘Do you see what’s happening here? Do you see how her coldness is behind his infidelity? Have you noticed the way his womanizing has undermined her confidence? Do you get it?’ . . . This is exactly what happens when you explain your dialogue to your readers”. Self –Editing for Fiction Writers, by Renni Browne & Dave King.
What Browne and King are talking about above is part of being an omniscient writer open to seeing the dialogue in front of you for what it is and what you want it to become in the eyes of the reader. Have you provided them with enough backstory, character traits, or plot details to infer by themselves? If you have, then you don’t need to explain it.
Tip: This is a big issue in much of the YA fiction submissions I read. Writers think they need to ‘dumb-down’ their writing for the teen audience and often write simplistic dialogue or explain the dialogue they have written. This is highly unnecessary and speaks to a lack of understanding of your audience. Who are you writing for? What is the market and what is their comprehension level? With YA there is cross-over potential so don’t alienate your readers by writing over-simple, explanatory dialogue.