It's hard to pick out what is relevant and what ain't.
Not really. The first half of City of God is basically a polemic against Roman paganism. The book was begun after the fall of Rome to Alaric and many of the pagans were arguing that the conversion of Rome to Christianity had angered the pagan gods and thus the barbarians had invaded and sacked the city. Augustine was responding to this. Most people today consider this the "boring" irrelevant half. The second half of the book is devoted to Christian theology and is thus considered by many to be the "relevant" half.