That's probably because it's rather cryptic and can be taken to mean lots of things. (Sun Tzu's The Art of War is similarly vague; I wouldn't recommend it for a military hand/textbook.)
I did read that a while back; my main impression was that it focused too much on the 'chessboard' school of warfare, and the mechanics of moving large numbers of men against other large numbers of men, while being general enough that, while insightful, it won't tell the professional officer anything he doesn't know: the points I remember most clearly are 'know thine enemy and know thyself, and in a thousand battles you will never be in trouble', 'use the ordinary force to hold the enemy (or words to that effect) and the extraordinary to destroy him' and 'avoid attacking élite troops'. These are all good sense, but they convey basic principles that you learn on a section commander's battle course: they might be useful in making generals out of amateurs, but they don't have much benefit in improving the quality of already-trained officers. What the junior officer needs is advice on leadership - how to work with his men, motivate them and get the best out of them - which I found sorely lacking.