"an object is a particular piece of memory, structured according to a class" does not sound like a particularly useful way to think about objects unless you are working at a low enough level that you care how objects are laid out in memory.
I don't particularly care how it's laid out. The point is that it is an instance of a class, which maintains its own local state - I don't care how that state is organized, but it's crucial to remember that it has such state.
