And now having read it I understand why it is held in high regard. Take a look at it through the link above. A few quotes give a feel for his pugnancious advocacy to not write lazily but do so with attention and concentration. His message is pretty similar to that of E.B. White in his Elements of Style or of Robert Graves in his The Reader Over Your Shoulder which I have always particularly enjoyed.
"A man may take to drink because he feels himself to be a failure, and then fail all the more completely because he drinks. It is rather the same thing that is happening to the English language. It becomes ugly and inaccurate because our thoughts are foolish, but the slovenliness of our language makes it easier for us to have foolish thoughts. The point is that the process is reversible. Modern English, especially written English, is full of bad habits which spread by imitation and which can be avoided if one is willing to take the necessary trouble. If one gets rid of these habits one can think more clearly, and to think clearly is a necessary first step toward political regeneration: so that the fight against bad English is not frivolous and is not the exclusive concern of professional writers."
I especially like his translation exercise.
"I am going to translate a passage of good English into modern English of the worst sort. Here is a well-known verse from Ecclesiastes:
I returned and saw under the sun, that the race is not to the swift, nor the battle to the strong, neither yet bread to the wise, nor yet riches to men of understanding, nor yet favour to men of skill; but time and chance happeneth to them all.
Here it is in modern English:
Objective considerations of contemporary phenomena compel the conclusion that success or failure in competitive activities exhibits no tendency to be commensurate with innate capacity, but that a considerable element of the unpredictable must invariably be taken into account."
And then later in the essay.
"A mass of Latin words falls upon the facts like soft snow, blurring the outline and covering up all the details. "