too difficult to understand

Re: too difficult to understand
My own interpretations...

When central banks design banknotes, they include on them details that make forgery difficult. These might include tiny lines and dots that are hard to see with the naked eye, and wavy or curly lines ("squiggles") which are difficult to reproduce without expensive printing equipment.

These banks have trained staff who can look at suspected forged notes and identify where the forger might have overlooked, omitted, or failed to reproduce correctly such details.

This idea is applied to the notion that governments' power over us, "authority", is exerted often by means of hidden tricks and methods.

A "secular patriot wrapped in the simple flag of self" evokes the idea of a simple minded person, with no spiritual or religious dimensions, who thinks about the world in a very self centred way, much as a stupid "patriot" is content to metaphorically "wrap the flag" around themselves to shield themselves from controversial or difficult thoughts.

a "professional descendant" makes me think of a person whose sense of their own identity is heavily dependent upon ideas of having ancestors from whom he or she is descended. Perhaps a bit like those British racists who say "This country has been white for thousands of years".

"The closed-for-the-holiday banks and post offices of the heart" sounds like he is accusing that sort of person of having an official, cold, regulated, unwelcoming (like a closed bank) personality or "heart".

The book you have chosen is a difficult one for many native speakers; its style is heavily idiosyncratic and poetic. I wonder if it is an appropriate choice for you at (what appears to be) your present stage of English learning.

Or maybe I have been fooled into doing you homework for you?