Milton is essentially penning an epic poem, a long narrative poem that details events which are important in the poet's culture and tells of big adventures and high drama. In ancient Greek epic poems, where the form originated in Western culture, the poet would typically begin with an invocation of the muse. The muses were nine daughters of Zeus, responsible for inspiring humankind to create various art forms. A classical poet would invoke the muse of epic poetry, named Calliope, asking her to inspire him and enhance his skill to tell his narrative, almost like asking for a blessing and divine aid. Milton seems to draw on this tradition, calling, it seems, on the Christian God rather than the ancient muse so that he can "assert Eternal Providence, / and justify the ways of God to men." Just as classical poets (like Homer, who was also blind, by the way) would call on the muse for divine aid, Milton seems to do the same thing so that he can do justice to the story he tells.