The title of Orwell's essay, "Politics and the English Language," suggests where the thrust of his thesis is; namely that language is "an instrument which we shape for our own purposes." 

Because language is a tool, politicians have molded it to their express designs; moreover, by employing euphemisms and a certain vagueness of meaning, political writing is able to both confuse the public, obfuscate facts, and mitigate wrongs, thereby convincing people of action(s) of which they would not approve if they were rightly informed.  

George Orwell supports his argument that language is manipulated by politicians to suit their exigent needs by the use of examples from various publications. One such example is that of number 4:

All the "best people" from the gentlemen's clubs, and all the frantic fascist captains, united in common hatred of Socials and bestial horror at the rising tide of the mass revolutionary movement, have turned to acts of provocation, to foul incendiarism, to medieval legends of poisoned wells to legalize their own destruction of proletarian organizations....

Orwell accuses the writer of using stale phrases such as "best people," "fascist captains," "rising tide." Then, in describing what the "best people" have done, the author of this passage is vague, using such stale and overworked metaphors as "acts of provocation," "foul incendiarism," and "medieval legends of poisoned wells" that also lack any specific meaning. In short, this politician wishes to get people emotionally charged without telling them anything specific, lest they disapprove and object.