This book makes the convincing case that caste is grievously misunderstood in the West. Usually, caste is interpreted as this transhistoric belief handed down from on high in the ancient writings of Hinduism and transmitted by belief and inertia among South Asia's Hindus.
I think the core segment of this argument is from pages 140 - 141: "It will be evident that I am deeply skeptical of attempts to trace socio-economic institutions to fundamental values. I have found considerable evidence to suggest that individuals systematically sough to modify and invent customs and institutions to their own perceived advantage, and that the patrimonial and early colonial state tried to derive fiscal and political advantage from these efforts. Inter-caste relationships and the idyllic village itself existed through the constant contest of unequal powers. The varying outcome of these ceaseless contests explains why institutions varied considerably at different times and in different regions. Society was never static in some "traditional" mode, and the bitter contests for political power and social status that rend the villages today are not as novel as they may seem".
As I understand it, the author makes the case that castes are bounded corporate entities that were constantly shaped by social and political forces. Caste is somewhat analogous to the corporate bodies found in feudal systems across Eurasia - we even call it "caste" because the Portuguese believed it vaguely analogous to their own systems with aristocrats and guilds, commoners and slaves, privileges and demerits. The author examines how castes developed - for example, how the trade castes formed as certain jobs became hereditary and passed down through family lines, or how people compelled to do unclean work became Dalits. The author highlights that this is based more in the material realities of power (and oppression) in South Asia than in just everyone "believing" in it strongly, and that despite being ruled largely by Muslims and Christians for the past half a millennium, both Islamic and European conquerors fit quite nicely into the pre-existing caste society. The author also explores how caste varied across India. Because castes are social/political categories, they could often not be recognized across the vast expanses of the subcontinent. The author provides the example of a Dalit from UP being treated as a Brahmin in Gujarat, or of how different groups of Brahmins did not recognize each other as valid. Finally, the author explores how caste changed over time. Apparently in contemporary times, there is less a focus on ritual purity even as the communal and electoral conflicts have heightened caste tensions.
I'll be perfectly honest - since I don't know a whole lot about India, there's a lot of stuff that I either missed entirely or that I probably misunderstood. That being said, the parts that I did understand are brilliant and changed my understand of how caste works - as a social construct shaped by contests over power, rather than just a belief manifesting in the social world.