So long as Christianity has existed, the question has been asked by believers and non-believers alike: Why does a loving God allow bad things to happen? An answer to this question by a Christian apologist is technically called a theodicy, and Paradise Lost is an extended example of one such argument.

Milton is by no means bashful in this regard. He openly states at the end of the poem's first stanza that he seeks to “assert th' Eternal Providence/And justifie the wayes of God to men.” He wants to show readers why the bad things that God allows to happen over the course of the poem—most notably Satan's corruption of humankind—is ultimately for the best.

Milton does this by drawing on the idea of the fortunate fall. This is the notion that the fall of humankind—which takes place in Paradise Lost after Adam and Eve defy God by eating of the Tree of Knowledge—is ultimately beneficial to humanity.

For had it not been for Adam and Eve's defiance and the subsequent introduction of sin and death into the world, then there would not have been a need for God to send His only begotten Son, Jesus Christ, into the world to save humanity. In simple terms, without original sin, there would've been no need for Christ.