One important lesson is that there is never one significant cause for massive changes. It is usually the case that many small changes compound on themselves until they finally "break the camel's back," and social or political changes are necessary.
The economy was a driver, but other factors did play an important part
"Enlightenment literature was not in itself revolutionary. [...] Disgruntled bourgeois did not make the French Revolution, but their dissatisfaction helped create a current of demands for reform. The monarchy's worsening financial crisis would accentuate these calls."
"Economic hardship compounded the monarchy's financial problems by decreasing revenue while exacerbating social tensions. High prices, falling wages, and high unemployment darkened the 1770s and 1780s."
The Declaration helped create a new way to measure a man: before, it was various privileges that you either had or could never have, and after, it was all based on wealth (similar to how modern social status functions).
"The Declaration thus helped make wealth, not birth, blood, or legal privilege, the foundation of social and political order in modern France."
While the French Revolution got rid of kings and queens, it inevitably led to the rise of the modern bureaucracy by moving more and more power into the hands of a centralized bureaucracy. Moreover, it also helped brew the idea that would dominate the following centuries: nationalism.
Government centralization
"These included in some places the abolition of feudalism, curtailment of clerical privileges, and more centralized government structure."
Rise of the "nationalistic feeling"
"The French presence engendered a patriotic response in some of the German and Italian states, contributing to the emergence of nationalist feeling there."
The title inflation of the French monarchy put a lot of pressure on its legitimacy
"The monarchy depended upon the sale of titles, offices, and economic monopolies for revenue and long-term credit. But by creating more offices — there were more than 50,000 in 1789 — it risked destroying public confidence and driving down the value of offices and loans already held."
Maslow, inequality, and universal laws
The Declaration introduced several universal laws, but unfortunately, these laws did not reduce society's inequality, which is often what most people care about (money tends to be closer to the bottom of Maslow's pyramid while freedom of speech tends to be quite further up).