The importance of this text cannot be overstated. Imam al-Ghazali draws our attention to several issues that common believers, and even those who are not believers, take for granted and hardly ever consider.
The main issue that the Imam deals with is that of carefulness, or wara', which comes in between that which is clearly lawful and clearly unlawful. And that being said, there are matters between the lawful and the unlawful that most people do not know.
According to Imam al-Ghazali, there are some matters that even scholars are unaware of. Once the reader has commenced, it should not take him long to see why the Imam was the most prolific scholar of his time.