Throughout the piece, Milton makes numerous religious and classical allusions (to the point of tedium). He considered the political freedom of ancient Greece to have been an ideal situation and attempts to link the greatness of Greece with the greatness of England. In addition, the Protestant Milton got a tremendous mileage out of continually evoking the frightening and hated visage of the Catholic Church, which had created in 1559 the infamous "Index of Prohibited Books".

Milton brings up three central points in his attack of censorship. Firstly, books are not the sole purveyors of evil or destructive information, so attempts to halt the flow of evil or destructive information by regulating book publishing would necessarily be ineffective. Secondly, you would need inhumanly perfect individuals to serve as judges, or personal biases and misunderstanding would creep into the system and damage the chances that "good" books had of publication. Thirdly, even "bad" books can serve a constructive purpose by strengthening an individual's resistance to faulty or evil ideas - if a person can be exposed to poisonous thoughts and triumph, their spirit will be the stronger for the contest.

"For Books are not absolutely dead things, but doe contain a potencie of life in them to be as active as that soule was whose progeny they are; nay they do preserve as in a violl the purest efficacie and extraction of that living intellect that bred them. I know they are as lively, and as vigorously productive, as those fabulous Dragons teeth; and being sown up and down, may chance to spring up armed men. And yet on the other hand unlesse warinesse be us'd, as good almost kill a Man as kill a good Book; who kills a Man kills a reasonable creature, Gods Image; but hee who destroyes a good Booke, kills reason it selfe, kills the Image of God, as it were in the eye. Many a man lives a burden to the Earth; but a good Booke is the pretious life-blood of a master spirit, imbalm'd and treasur'd up on purpose to a life beyond life."