In some ways, this question points toward one of the common misunderstandings of the French Revolution. There's a tendency among many to cast the Third Estate as the sole driving force of the French Revolution. The historical reality is significantly more complicated than that picture would attest.
Before getting to that point, however, I think you should keep in mind that the Estates System, taken as a whole, represents a social structure. That was the foundation of the Ancien Régime, and ultimately, that structure was what the Revolution dismantled: an entire system of privilege and particularities was swept aside by a more modern political understanding based in equality under the law. From this perspective alone, the Estates are deeply important to the French Revolution.
Ultimately, I think there is a tendency to underestimate the liberalism which existed within the Second Estate, viewing it (along with the First Estate) as a collection of reactionaries, opposed to the Third...
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