To handle a language skillfully is to practice a kind of evocative sorcery.—Charles Baudelaire
You need to be able to communicate with other people. For that, both parties must share a common language—which can be verbal, written, sign, or anything else they both understand. Even without a shared formal language, two strangers can exchange basic ideas through body gestures.
The shared level of understanding determines the degree of communication that can be achieved. But in some cases, understanding the pieces doesn’t mean understanding the whole. You can be talking to someone for a long time—believing yourself in full rapport—only to realize you’ve completely misunderstood an underlying premise.
It is the role of an editor to work with an author to effectively communicate ideas to an audience. This is accomplished by applying certain standards and styles of communication, and by simply acting as a second pair of eyes to spot any areas that can be improved.