In Nature, what does Emerson mean when he talks about a "poetical sense" of looking at nature?

As always, it is
particularly important to look at quotations in context to help us be aware of what the author
is trying to say by including them in their writing. In this case, if we have a look at the
lines immediately after the quote you refer to, we can easily see the meaning that Emerson is
trying to attain through talking about the "poetical sense" of looking at nature and
the way that it contrasts with the normal human way of regarding the natural world:

It is this which distinguishes the stick of timber of the
wood-cutter, from the tree of the poet. The charming landscape which I saw this morning, is
indubitably made up of some twenty or thirty farms. Miller owns this field, Locke that, and
Manning the woodland beyond. But none of them owns the landscape. There is a property in the
horizon which no man has but he whose eye can integrate all the parts, that is, the
poet.

To look at nature with a "poetical
sense," therefore, is to see it in a way that "integrates" all of nature and does
not regard nature in a way that is purely functional or seen in relation to man's posessions and
interests. Emerson uses two examples where he talks about the wood-cutter who only sees a
"stick of timber," whereas the poet is able to see the "tree." He then talks
about farms that are measured and cut off from each other and owned by different families. The
poet is the only person, Emerson argues, who is able to "integrate" all of these human
divisions and see nature in its wonderful entirety.