The book takes you though the essential topics and main objects in Cocoa, without which you cannot make any progress.
There is thorough and authoritative grounding given, using sample projects that demonstrate how these objects are applied. Although not an exhaustive reference work, there is enough to spark interest for further research and to give an understanding of the principles involved.
This is a new topic for many and this book goes a long way to ease the transition from novice to being able to write Objective-C programs under your own steam.