What can people infer by reading the last line of a Midsummer Nights Dream?

Puck’s final line asks for applause and references his earlier statement that if the audience didn’t like the play, they can pretend it was just a dream.

Give me your hands, if we be friends,
And Robin shall restore amends. (Act 5, Scene 1)

Puck, or Robin Goodfellow, is breaking the fourth wall, or the invisible barrier between the audience and the actors.  He directs his speech to the audience as a way of bringing up again the concept of dreams.  

If we shadows have offended,
Think but this, and all is mended,
That you have but slumber'd here
While these visions did appear.
And this weak and idle theme,
No more yielding but a dream … (Act 5, Scene 1)

In other words, a play is like a dream.  The action in this play in particular has many elements of fantasy.  It does seem like something one might dream.  A play is a dream shared by the actors and audience.  It is a real magic, because plays entertain us and bring us to a place we would not otherwise be.

Throughout the play, Puck does silly things for Oberon’s benefit and probably was one of the audience’s favorite characters.  Elizabethans believed in sprites and fairies, and Shakespeare often used them to add a magical element to his plays.  Prospero makes a similar speech at the end of The Tempest.

Let me not,
Since I have my dukedom got
And pardon'd the deceiver, dwell
In this bare island by your spell;
But release me from my bands
With the help of your good hands ... (Act 5, Scene 1)

Prospero implies that the audience releases the actors with their applause.  When Prosper says, “Now my charms are all o'erthrown” it is a reference to his character, as a wizard, and also to the spell the actors have during the brief time that they are on stage.  Puck and Prospero both are telling the audience that they can thank the actors and go, because the spell is broken.