Think it might be she cares about ismene and doesnt want her to suffer or she promised her father that she will protect ismene
An introduction is given about how the topic of interes will be treated.
Usually images of an explanatory nature are included, with a explanatory talk, the images are included to bring the reciver closer to the topic of interest in a friendly way.
it's purpose is to inform a non specialized public, and sometimes, without prior knowledge, so that the same present an interest in the subject.