In order to fully understand these lines from Pope's verse discourse An Essay on Criticism (1711), a seminal exploration of Neoclassical poetic ideals and literary criticism, we need to look briefly at Pope's argument with respect to both good poetry and good criticism, both of which are subjects of the Essay. From Pope's perspective, poetry and those who interpret poetry are inextricably bound, and between bad poetry and misinterpretation of that poetry, the misinterpretation can be the most harmful:
'Tis hard to say if greater want of skill
Appear in writing or in judging ill
But, of the two, less dang'rous is th' offence
To tire our patience, than mislead our sense (I:1-3).
In short, criticism that misinterprets a poem is more dangerous than a bad poem because it leads readers astray.
Pope, having come of age at the beginning of the Neoclassical Period in English literature, is not only steeped in the classics but is himself a Neoclassicist. He believes that the essence of good writing requires that the poet must
First follow NATURE, and your judgment frame
By her just standard, which is still the same:
Unerring Nature, still divinely bright,
One clear, unchang'd, and universal light,
Life, force, and beauty, must to all impart,
At once the source, and end, and test of art (I:68-73).
By nature, Pope and other Neoclassicists mean not only that which is created by God but also that which is unalterably good and true. For the Neoclassicists, this conception means that poetry must exhibit: natural, uncluttered language; a natural poetic rhythm for English, which is iambic pentameter; decorum; economy in expression (the heroic couplet, for example); and, most important, poetry, in its finest expression, both instructs and delights the reader. Whatever one thinks of works like An Essay on Man, An Essay on Criticism, or The Rape of the Lock, they can be said to be instructive and delightful at the same time.
Part II of the Essay contains the lines in your question, and these lines are addressed to the literary critics who do not focus on the foundational ideals of Neoclassic poetry and are therefore likely to mislead readers:
Others for language all their care express,
And value books, as women men, for dress:
Their praise is still—"the style is excellent":
The sense, they humbly take upon content (II:305-308).
In other words, critics focus on the outward appearance of a work--like women who evaluate men by their dress--and these critics mistake the appearance for the meaning of the work. Their judgment, then, that the "style is excellent" is not a judgment of a work's intrinsic meaning or value but a valuation based on criteria that have nothing to do with those things that are unchangeably good. Pope is arguing that such critics are fooled by appearances and therefore fail to explore the meaning inherent in the work.
Pope's focus on flowery language as a primary problem is clear when he says
Words are like leaves; and where they most abound,
Much fruit of sense beneath is rarely found (II:309-310).
Pope points out here that profuse language often makes understanding difficult or impossible, using the simile of leaves covering up fruit as a visual aid. As I noted above, one of the elements of Neoclassical poetry is the heroic couplet, a rhyming couplet in iambic pentameter that is, because of the natural word order and flow of English, a powerful vehicle for compressed poetic expression. And if we look at the diction that Pope uses most often in the Essay, we will find that short words of one or two syllables predominate, another element preferred by the Neoclassicists because such words are readily sensible. If one is writing to instruct and delight, vocabulary must be kept as simple and straightforward as possible. Like the sun shining on our surroundings, clear and uncluttered language facilitates our view of what we read.
These lines, then, encapsulate a main point of An Essay on Criticism—that meaning is often lost in overwrought language, and critics who focus on "presentation," as opposed to the underlying meaning of a work, will inevitably not only misinterpret a work but also lead readers to the same misinterpretation.