In keeping with the poem's didactic tone—that is to say, Pope's trying to teach us something—Pope uses appropriately authoritative language to get his point across. For instance, in the most famous line of the poem "Whatever Is, is RIGHT," it's no accident that the first "is" is capitalized and the word "right" is written in block capitals. This is a way for Pope to emphasize the significance of the point he's making. Essentially, what he's saying here is that, no matter how much evil and suffering there is in the world, God is still firmly in charge.

Also significant in this regard is Pope's use of anaphora. This is a rhetorical device in which a sequence of words is repeated at the beginning of neighboring clauses. One of just many examples in literature comes from Wordsworth's Tintern Abbey:

Five years have passed;
Five summers, with the length of
Five long winters! and again I hear these waters… (Emphasis added).

The repetitive nature of anaphora drives home the relevant argument. And in An Essay on Man we find Pope resorting to this rhetorical device to persuade us that our perspective on things is partial, and that the full picture is known only to God:

All Nature is but Art, unknown to thee;
All Chance, Direction, which thou canst not see;
All Discord, Harmony, not understood;
All partial Evil, universal Good[.]

"An Essay on Man" by Alexander Pope is an outstanding example of Augustan poetic style. It is written entirely in relatively regular end-stopped heroic couplets and yet, despite this, maintains a fairly natural and fluid rhythmical patterning. 

The very regularity of the poem's rhythm and rhyme scheme suggest to the reader the ideal of calm rationality that Pope espouses. The rhythmical shape of the lines enhances the periodic style and balanced clauses to present the reader with a sort of ordered linguistic universe that recapitulates Pope's sense of cosmos. 

Pope's poem exemplifies what the poet and critic Donald Davie advocated in his Purity of Diction in English Verse, a use of ordinary language that was direct and clearly readable, showing restraint in its use of poetic effects and figures and avoiding the recondite and obscure. Pope's language is distinguished by its clarity and precision and the way he approaches abstract concepts directly rather than through the abstruse metaphors of the Metaphysicals.