Epigraphs are like little appetizers to the great main dish of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
Oh, the torment bred in the race,
The grinding scream of death
And the stroke that hits the vein,
The hemorrhage none can staunch, the grief,
The curse no man can bear.
But there is a cure in the house,
And not outside it, no,
Not from others but from them,
Their bloody strife. We sing to you,
Dark gods beneath the earth.
Now hear, you blissful powers underground –
Answer the call, send help.
Bless the children, give them triumph now.
(Aeschylus, The Libation Bearers)
Death is but crossing the world, as friends do the seas; they live in one another still. For they must needs be present, that love and live in that which is omnipresent. In this divine glass, they see face to face; and their converse is free, as well as pure. This is the comfort of friends, that though they may be said to die, yet their friendship and society are, in the best sense, ever present, because immortal.
(William Penn, More Fruits of Solitude)
OK, first up: Aeschylus (spell that ten times fast). The Libation Bearers is the second play in a trilogy called the Oresteia (originally performed in Athens in 458 BC), which depicts the fall of the house of Atreus after the Trojan War. This particular play by our man Aeschylus is all about revenge – in The Libation Bearers, the murdered King Agamemnon's son, Orestes, returns home after years in exile, and, along with his sister Electra, plans to exact vengeance for the death of his father. Unfortunately, the murderer is none other than his mother, Clytemnestra, which leads to a whole new chain of consequences (detailed in the third play, The Eumenides – but that's another story). Why, you may ask, would Rowling reference this rather grim tale? Well, aside from the obvious revenge narrative going on here (Harry is avenging his parents, and everyone else that Voldemort killed), there's also an appeal to death going on. Oddly, this passage asks the gods of death and darkness to "bless the children" and help them on their mission.
Speaking of odd relations to death, let's look at the William Penn quote too. This second epigraph is a somewhat sweeter message with a similar theme. Penn reminds us that the dead never really leave us (and in a good way, not in an undead, zombie kind of way); rather, they're with us in our hearts always. Basically, if you love someone, a part of him or her will always be with you, no matter what happens.
Both of these epigraphs speak to the most significant theme of Deathly Hallows – the pressing need to confront the boundary between life and death, which turns out to be less solid than you'd imagine. In this final book, Harry comes to terms with everyone and everything he's lost; the question is, how much can he draw upon those people, even though they've departed this world?