Words are odd things. They don't just create meaning - they also create feeling.
When a text is created (including your own - which means whenever you write or speak!), some of its words and phrases will have been carefully chosen to appeal to the audience and so achieve a purpose.
A key skill you need to develop is to be able to identify the important effects a writer creates within a text and then be able to explain HOW these effects were created (that is, the method used, e.g. a vivid metaphor, powerful imagery, alliteration, use of rhyme or rhythm, etc.) and to suggest WHY the effect was created, both 'locally' at the point in the text where it occurs as well as how this one effect contributes to the text's overall meaning (that is, as part of a structure).