As to Foucault's Works

 As to Foucault's works

His book is difficult to read because it consists of long, rambling sentences and the main points are unclear.

Aren't there a lot of people who say things like that?

As to his word

"Where there is power, there is resistance."

This is simply stating the perfectly obvious fact that every action has a reaction.

"The soul is the prison of the body."

It implies that the body and mind are interconnected; regardless of which one you take as the subject, you are essentially saying the same thing.

Could the lack of conceptual precision be due to the limited vocabulary of the French language?

Conclusion

Philosophers ought to clearly convey what they have understood to their readers.

So, for the 10% he couldn't understand himself, he adopted a style of inviting the reader to think about it along with him - I see, that makes sense.