HI Anujit, the book is definitely about using Scala as the vehicle for purely functional programming. In many ways, the book is not 'about' Scala, we are just using Scala as the vehicle for teaching FP, though you will certainly learn Scala as a consequence of working through the book. That said, though our main goal is teaching FP, when we introduce new concepts / techniques, etc, where it makes sense we try to motivate and relate these things for someone coming from a more traditional OO background. Many of the part 1 chapters are 'relearning' the functional way of doing something that people already know how to do in imperative programming, and we definitely try to make the connection that although FP is different, it is not totally disconnected from what you already know. Parts 2-4 get into territory where there isn't as much of an analogue to other types of programming - much of that will be specific to FP and very new to people.
You can check out the preface (free online, along with chapter 1) here:
http://manning.com/bjarnason/FPiS_meap_ch01.pdf It talks about what the goals of the book are, who the audience is, and how it is organized.