I sung of Chaos and eternal Night
Taught by the heav'nly Muse to venture down
The dark descent, and up to reascend...
This sounds fun, huh? Get ready to descend into hell. Turn the page, and the first chapter is titled Pandemonium, another Paradise Lost shout-out. This epigraph lets us know that we, with Clary, are about to travel into a dark world. There's hope, though: "Up to reascend." So we won't be down there forever. We'll come back. We hope.
Also, one thing to remember is that Milton was blind. Clary, and all mortals, are blind, too, in a way. They're blind to the magical worlds that lie right in front them, masked by a magical veil, keeping them safe (or at least unaware) of angels and demons that live among us.
Facilis descensus Averno;
Noctes atque dies patet atri ianua Ditis;
Sed revocare gradum superasque evadere ad auras,
Hoc opus, hic labor est.
—Virgil, The Aeneid
If you know how to say, "What you talkin' 'bout, Virgil?" in Latin, you probably don't need our help with this one. You know this is from Book 6 of The Aeneid, and it says, "The way downward is easy from Avernus. Black Dis' door stands open night and day. But to retrace your steps to heaven's air, There is the trouble, there is the toil" (6.187-190).
The idea here is that a whole lot of people die. But a very small number (if any) ever come back from that. So the way down is a piece of cake. The gist? Part Two is beginning, and things are about to get dark and dangerous.
The descent beckons
as the ascent beckoned.
—William Carlos Williams, "The Descent"
Well, this is a lot more straightforward than the last epigraph, isn't it? It's in English, for one thing. And it's only two lines. We can totally handle that.
William Carlos Williams is a master of condensing meaning into very few lines. Quoting him makes for the perfect epigraph for Part 3, which sees muddled pasts get cleared up and Clary's quest gain an intense, immediate focus as the plot barrels through to the finish line.
It also does a wonderful job of echoing the previous two epigraphs. Descent, ascent, descent, ascent. It's like an opposites lesson from Cassandra Clare. Maybe she can team up with Katy Perry for a follow up to "Hot N Cold." But seriously, it also lets us know that the ascent isn't going to happen yet. Maybe not even in this book. The descent is what is immediate, and maybe the ascent has already passed us by.