Henry V is one of Shakespeare's most self-conscious plays. Each time the Chorus steps out on stage to set the scene for us, we're asked to pardon the theater's inability to accurately portray historical events (like Battle of Agincourt, the siege of Harfleur, and Henry's journey across the English Channel). After all, it's impossible for a tiny theater stage to "hold the vastly fields of France" or the thousands of troops and horses that marched across the battlefields. Time and time again, the Chorus suggests that the audience must labor alongside the actors (and soldiers). By using our imaginations, we, the audience, are responsible for bringing Shakespeare's play to life. The fact that Shakespeare sees his play as an interactive experience is pretty cool, don't you think?
By constantly referring to the theater's shortcomings, Henry V reminds us that what we are watching on stage (or reading) is not real, but is in fact a dramatic portrayal of history.
The Chorus is one of the most important figures in Henry V because the character's function is to set the stage for the audience and to comment on the play's most important themes.