Into this wild abyss,
The womb of nature and perhaps her grave,
Of neither sea, nor shore, nor air, nor fire,
But all these in their pregnant causes mixed
Confusedly, and which thus must ever fight,
Unless the almighty maker them ordain
His dark materials to create more worlds,
Into this wild abyss the wary fiend
Stood on the brink of hell and look a while,
Pondering his voyage...
–John Milton, Paradise Lost, Book II
Paradise Lost is an epic poem by John Milton, written in the 1600s. It's kind of the epic poem to end all epic poems, telling the Biblical story of Satan's fall and Adam and Eve being booted out paradise (a.k.a. the Garden of Eden). The poem has become one of those literary giants that people quote, reinterpret, write books about, and generally make a big fuss over.
The section of Paradise Lost featured here is from Book II, which tells about Satan's attempt to find the other world God created that had been told of in prophecy and tradition. In the epigraph's quoted lines, Satan stands on the brink of Heaven and Hell and contemplates his journey. Sound familiar? This definitely reminds us of Lord Asriel breaking into another world. (See "Characters: Lord Asriel" for more.) The line "His dark materials," which Pullman uses as the name for his trilogy, refers to the materials the "almighty maker" (God) uses to create new worlds.