It's supposed to describe in detail what the patent claims as an invention, but it's not supposed to give complete engineering details. It's supposed to tell you what he's done and how that is unique, but the reason he's allowed to keep his patent is because he's told you what the law requires him to tell you. The idea behind this is to promote technological progress.

If you're smart enough to understand what he's done, you can take his idea and improve on it. The patent is supposed to further progress but not promote reverse-engineering. If you replicate even in a very general sense, what he's done, without improvement or major changes, you're subject to infringement penalties.

Of course, it's up to him, the inventor and patent-holder, to protect his patent. His patent may also expose him to suit by prior inventors. The patent office sometimes fails to notice that.

RE