"Not necessity, not desire - no, the love of power is the demon of men. Let them have everything - health, food, a place to live, entertainment - they are and remain unhappy and low-spirited: for the demon waits and waits and will be satisfied"

The quote suggests that it's not standard requirements or yearnings that drive guys, however rather a love of power. Even if human beings have everything they need and want, they will still be dissatisfied because the desire for power will always be lurking and waiting to be satisfied. This insatiable desire for power is represented as a "devil" that manages guys and eventually causes their distress.