The Party is basically a government-affiliated old boys club. While one doesn't necessarily need Party connections or membership to become successful, they open doors. For example, there is a Party committee in many publicly traded Chinese corporations. While the Party committee doesn't control the company directly, they have the power to hire and fire people and are more likely to hire Party members or people they have special relationships with to leadership positions in the company. So, while the Party doesn't force all it's members to be perfect, law abiding citizens, it does keep them from wanting a big shake up of the status quo.
I got this information from a book called The Party: The Secret World of China's Communist Rulers by Richard McGregor.
A little dated at this point, but still the best introduction I've read: https://smile.amazon.com/Party-Secret-Chinas-Communist-Rulers/dp/0061708771/
Atrophy and Adaptation is good, but very academic.
This is pretty much the best book. Informative and readable.