"His dark materials to create more worlds"

The fall of Luciferii - Paradise Lost
Public DomainThe fall of Luciferii - Paradise Lost
This quote is taken from Paradise Lost, an epic poem by John Milton. It was originally published in 1667.

The poem concerns the story of Adam and Eve and the Fall of Man, as the two original humans are tempted by the fallen angel Satan and expelled from the Garden of Eden.

It is no straightforward retelling of the Genesis story, however. Paradise Lost features Satan in several guises that present him as the hero. He is certainly a more interesting character than God, which has led critics to question whether the poem is in fact a criticism of the church's power.  

Satan's expulsion from Heaven
Public DomainSatan's expulsion from Heaven

This is very relevant to Northern Lights, with its depiction of the omnipotent "Magisterium" and the crimes that its power allows its authorities to commit. 

The opening quote from Paradise Lost contains the title of the trilogy as a whole: "His Dark Materials". Pullman was greatly inspired by John Milton's work, and intended the trilogy to be a reflection of Paradise Lost – a battle between Heaven and Hell, with the devil in the role of the hero.