The Essential Golden Dawn is the best book a beginner can read on the subject. It is also the best for someone who wonders if this tradition is good for him. I can say that it is the best introduction to the subject.
The book is written by the very famous adepts and pioneers of the Golden Dawn revival, the Ciceros, in a plain, easy and well-structured way. Its intent is to present and not analyse, the system of the Golden Dawn, the history of the order, the influences of the system, the grades, the basic occult sciences that it teaches and what someone could expect to learn or gain at any level. There is also basic information on how magick works, what is medieval magick, renaissance magick, theurgy and lastly, what is the Golden Dawn magic. There are also good advice and excerpts from the Golden Dawn material that helps document their views. As for the practical aspects, there is a brief description of the LRP, the Middle Pillar, invocations and the basic structure of a Golden Dawn ritual. In the last chapter, there is good information on self-initiation, ego-inflammation, and the path of the true initiate.
This isn't a book for rituals, but it will provide a good theoretical base to know about the system, what has to offer, what to expect and how to proceed. It is a small and concise book, which means that the information is zipped in the paragraphs. So, the reader who has no idea on the Golden Dawn he won't understand it completely. He has to search a lot of things online and it is for sure that the reader who wants to completely understand it, he will return to the book 3-4-5 times to read it again. Keep it on a shelf that you are going to reach easily. You can guess the condition of my book from the photo.
Theurgy and Philosophy are two different methods which lead to the union with God.