* The Four Worlds of the spiritual realm
By Rabbi Yosef Y. Schneersohn, the Previous (6th) Lubavitcher Rebbe (who passed on 10 Shevat in 5710 / 1950). This book explains the progression and nature of the created spiritual worlds. It uses precise analogies that make knowledge of the non-physical realm of existence accessible to the human intellect. It includes extensive explanatory footnotes. The tutorial Appendix make this one of the best places to start for learning about the worlds of Atzilus, Beriah, Yetzirah and Asiyah.
To download this book as a free PDF file, CLICK HERE
Here is another book by the Previous Rebbe that we recommend on Asknoah.org:
The Principles of Education and Guidance (free to read on-line)