Most work on terrorism approaches it from what you mind call the Clausewitzean lens: war as a continuation of policy by other means. Political scientists especially focus on terrorism as a rational strategy or a "weapon of the weak," a way for small groups to wage asymmetrical warfare, garner attention, shift national or international politics, etc. There's certainly a lot to be said for this approach, but MJ in this book unpacks a different approach to terrorism from the perspective of sociology, semiotics, and religious studies.
MJ approaches terrorism as an activity of meaning-making and assertion as much as rational political strategy. He does so through 5 case studies of terrorists around the world: white nationalists and anti-abortion terrorists in the US, Sikh terrorists in India, Palestinian terrorists like Hamas, Jewish terrorists like Baruch Goldstein, and Aum Shinrikyo in Japan. He shows similar mentalities, styles, and trends in each of these. For example, are all reacting in some way to political, social, and cultural change by leaning back on fundamentalist religion and making war on representatives of change. They are asserting the superiority of the permanent and transcendent over the new and mutable.
On a deeper level though, MJ shows that terrorism isn't just about strategic calculation. It is cultural and social activity deeply woven with meaning and narrative. Religious terrorists are responding to what they see as a disordered cosmos: something has gone fundamentally wrong, the rightful laws or rulers have been usurped, corruption and decadence are spreading, and their people have become lost and dispossessed. Religious terrorists see themselves as soldiers of what MJ calls cosmic wars, wars between essential good and essential evil that transcend their individual lives. They fight against dehumanized, shadowy enemies, and this combined with the cosmic war concept makes them more willing to shed massive amounts of blood than secular terrorists. Each terrorist attack is supposed to be an event in which the dispossessed group asserts its dignity, spreads its message, and defies an evil and oppressive authority (at least in their eyes). For example, the Aum sarin attack really had no strategy behind it. It was all about triggering the apocalypse and registering their hatred of bourgeois Japanese society; similar things can be said about other terrorist attacks.
For the individual terrorist who is likely (or certain) to die in their attacks, strategic calculation is even less important. Rather, they seek meaning within a grand cosmic narrative and escape from tawdry, often meaningless lives. It isn't necessary poverty that makes terrorists but a sense of liminality: it isn't a coincidence that such a large number of terrorists are single young men. They lack but desperately want a place in society but do not yet have a permanent job, a spouse, a family, and positions of authority. For the serious but adrift young man, radicalism can be a short-cut to transcendent meaning. This kind of radical altruism (that is also ultimately self-serving) is what helps create the young terrorist. The group and leadership may be calculating and rational, but I think that MJ's more meaning-based approach is more useful for studying the motives of individual terrorists.
One thing I'd like to take from this book to apply to my own research is to look at how counterterrorists, broadly construed, also see terrorism as a manifestation of a broken, disordered universe and how that belief plays out in their policies, rhetoric, etc. Terrorism is such an extreme form of human violence that I think it provokes intense feelings and grand narratives on both sides, and I'd like to unpack historically how counterterrorists have also made meaning from their actions, linked CT to other issues, and forged narratives to try to understand what is happening to them and what they are doing in response. In short, I'm not saying that rational policy making doesn't exist but that it's very hard to not engage in the human activities of meaning making, symbolism, and narrative.
I didn't love everything in this book. I thought the organization was a little ineffective: 5 case study chapters followed by 4 thematic chapters exploring the nature of religious terrorism. This got a little repetitive. I'm also not all that convinced that religious terrorism is necessarily worse than secular terrorism, although some major attacks since the 1990s suggest that it might be because of a tendency toward Manichean and cosmic thinking.