Short and gets right to the point. It's about discerning spirits, but also talks about the importance of worshipping at spirit filled church. This book is full of relevant scripture. It really made me wonder why most of the churches I've visited do not talk about discerning spirits, spiritual warfare and welcoming the holy spirit into your life.
This is a less than 50 page book that can be read in one setting. 1 John 4:1-6 is the focus of the book and it stresses the importance of testing the spirits and not the person within the five-fold. Some will say there's need for the Bible, or some will use it with no knowledge (and/or fruit). The key to testing the spirits is to rely on Holy Spirit to guide you into the spirit or truth so you can discern the spirit of error. If you know someone who can be deceived or if you have been deceived before, this is worth a read.