To my mind, the part of the narrator is fundamental. Typecasting should be avoided. Once again, choosing the narrator is crucial. Though each line has a rhythm somewhere near to iambic pentameter, none should be read to bring out that metre at the expense of meaning. These must be read for meaning, the authority of biblical speech-act, the triple judgments of Book X. 5.
Meaning dominates metre here as well.
Book One Narrator Of man's first disobedience, and the fruit Of that forbidden tree, whose mortal taste Brought death into the world, and all our woe, . . . Sing heavenly Muse . . . The infernal serpent, he it was, what time His pride had cast him out from heaven . . . To bottomless perdition . . All is not lost.