Milton gives the example of how The Bible details the blasphemous and evil-doings of bad people as a way to show the righteous path of God. Undeniably, good and evil must be intertwined together for virtue to even exist, because "the scanning of error" only "confirms the truth," and the only other way to theoretically partake of bad/evil without actually doing so, was through literature that portrayed poor choices and characters. The complexity and power of this argument Milton makes, not only paints censorship as a limit on learning, but also as a hinderance upon virtue. For a long time, the story of Adam and Eve was perceived as a narrative about the loss of innocence and the punishment we all live face because of this, but it had failed to even consider that innocence or total ignorance were not the same thing as virtue.
By recognizing good by and through the presence of evil, virtue was fostered in a way that was pleasing to humanity and God. Virtue was such a lauded abstract principle that was rarely seen as the twin of vice, neither one could exist without the other.