Officials have power. How do we protect the citizens against its abuse?

Two ways:

From above, through hierarchy and responsibility. From below, through the rights of local communities and corporations. Control from below makes up for what control from above does not reach.

The sensitive point:

In the conduct of officials, the laws touch the individual citizen. This point decides whether the citizens trust the government. How officials carry something out often counts as much for citizens as the content itself.

A danger:

Officials can band together as an estate. Against the citizens and against their superiors. Then the sovereign himself may have to step in. Frederick the Great did this in the case of the miller Arnold.

Summary: Control from above and the rights of local communities from below protect against abuse. The conduct of officials decides whether the citizens have confidence. If need be, the sovereign must step in.