How would you critically explicate lines 1-26 of Book I of John Milton's epic poem Paradise Lost?

Lines 1-26 of Book I of John Milton’s epic poem
Paradise Lost are particularly important because they announce many
of the most important themes of the poem as a whole. They also exhibit some of the
techniques, and some of the crucial words, that Milton will employ throughout the poem.
The first line, for instance, speaks of “man’s first disobedience,” referring to the
very first sin, committed by Adam and Eve in the Garden of Eden. This, of course, is a
chief theme of the entire work. Yet already Milton is playing with words, since the word
“first” implies both the priority of this sin in time as well as its crucial importance:
it was the most significant of all sins precisely because it was
the first and thus provided a pattern for every other subsequent sin. Similarly, when
Milton refers to the “fruit / Of that forbidden tree” (1-2), he puns on the word
“fruit,” referring both to the literal fruit tasted by Adam and Eve as well as to
everything that resulted from their eating of the fruit.

In
line 3, the speaker of the poem announces that the taste of the fruit “Brought death
into the world, and all our woe.” Death, of course, is another main theme of this poem,
but note that Milton uses phrasing normally associated with birth (when he speaks of
something being “Brought . . . into the world”) when he paradoxically announces the
birth of death. The first sin was also responsible for “all our woe” – a phrase that
splendidly uses assonance and heavily accented monosyllables to draw out the length of
the phrase and thus issue almost a cry of pain. The word “woe,” moreover, will be used
frequently throughout the poem, as will the word “all,” so that Milton is here
emphasizing key parts of his subsequent vocabulary.

Note
that it is not until line 6 that the verb “Sing,” on which all of the first six lines
depend, eventually appears. This kind of unusual sentence structure is often found in
Latin sentences but rarely in English, but Milton deliberately wanted to imitate a
so-called “Latinate” syntax in this poem. Milton’s “invocation” to (or calling upon) the
“Heav’nly Muse” (6) shows his desire to write a Christian epic while still using many of
the formal devices of a classical epic. Invocations to the muses were common in the
earliest Greek and Roman epics, and Milton is here showing his typical desire to imitate
the classics while also, in a sense, surpassing them.

Many
more aspects of the first 26 lines might be mentioned, such as the biblical allusion at
the beginning of line 9, the echo of an Italian epic in line 16 (a line in which Milton
paradoxically proclaims his desire to be original), and the emphatic statement of the
key theme of the entire poem in line 26 itself. Milton’s invocation is simultaneously
assertive (12-16) and humble (22-23) in a way that is characteristic of the poem as a
whole.

For an excellent brief overview of the poem, please
see C. S. Lewis, A Preface to Paradise Lost (Oxford: Oxford
University Press, 1961).