Augustine knew of the contingencies of writing and readership. Some people, he says at the beginning of The Trinity (1.1.5) will not be able to understand what he writes, but there are others who could understand but will never encounter his book.
That’s “why it is useful to have several books by several authors, even on the same subjects, differing in style though not in faith, so that the matter itself may reach as many as possible, some in this way others in that.”
Some readers, though, are virtually hopeless: They complain that they don’t understand Augustine, but also admit they’ve never understood any of the other books on the topic either. They need to be silent and devote themselves to serious study rather than tossing “querulous abuse” at writers.