Narration is a very valuable tool in drama. It's uses are manyfold. To begin with, a narrator acts as a single omniscient and omnipresent character who is able to comment, much like a Chorus.
A narrator can do the following:
As an extension activity, try this:
If I were you
At a critical moment in a character's life when a decision must be made, a dilemma, problem or choice must be faced, the character walks between two rows of students who provide an external commentary on how others see the character's situation by offering advice or comment as the character passes.
At its best, a narrator can comment on an actor or situation that is taking place on the stage.
The play, 'The Rocky Horror Show' does this to hilarious effect.
Tip: Try not to take the narrator too seriously. They can also be used to their greatest effect if they provide a break from the tension of the drama.