"Evil, Be Thou My Good"
Context: In the Argument to Book IV of Paradise Lost, Milton notes that Satan is filled with doubts upon first regarding Eden and contemplating his second act against God, the seduction of mankind, but that Satan pulls himself together and "confirms himself in evil." The context of this, line is important, then, to the structure of Milton's poem. This is the point at which Satan, once a great angel in Heaven, puts aside any hesitation and makes the decision which is to influence the rest of the action of the poem. In so doing, of course, Satan has to turn things inside out: he must reject good as evil and accept evil as good. This act he does:
"So farewell hope, and with hope farewell fear,Farewell remorse: all good to me is lost;Evil be thou my good; by thee at leastDivided empire with heaven's king I holdBy thee, and more than half perhaps will reign;As man ere long, and this new world shall know."