PUCK
Now the hungry lion roars,
And the wolf behowls the moon,
Whilst the heavy ploughman snores,
All with weary task fordone.
Now the wasted brands do glow,
Whilst the screech-owl, screeching loud,
Puts the wretch that lies in woe
In remembrance of a shroud.
Now it is the time of night
That the graves, all gaping wide,
Every one lets forth his sprite
In the church-way paths to glide.
And we fairies, that do run
By the triple Hecate's team
From the presence of the sun,
Following darkness like a dream,
Now are frolic. (5.1.388-407)

Puck draws attention back to the darkness of the play.  In the courtly world, the feuds have ended, the lovers have all wed, and everything seems to be moving toward a happily-ever-after. Puck reminds us, though, that another reality still exists, one where nighttime is not for lovemaking and fairies, but for terrifying animals and the dead.  Puck is the perfect candidate to make this reminder, as he is neither fairy nor human, but one who straddles both worlds and thus has an arguably more objective perspective about each of their versions of reality.