I'm not too sure but I will try. An abstract painting is a painting that isn't very clear to people or that doesn't depict a clear image (It doesn't make much sense to anyone but the person who drew it). When people remember stuff sometimes it isn't very clear, or if they try to explain it to someone else the other person doesn't understand it well, So all in all, I believe the author is trying to say that a memory is usually unclear or foreign to anyone but the person who had that memory.
The character that best brings out the theme of a thirst for
knowledge and the undiscovered would probably have to be Dr. Frankenstein
himself. This is so because it is he who
creates the monster out of his thirst for discovering the undiscovered, and it
is his action of creation—being the creator—that illustrates his knowledge and
thirst of it.
