What does the decreasing line length represent in this stanza

This rocky canyon in the desert is not the deepest canyon or the whitest which best identifies the adjective phrase

It's to know your purpose before you read something because a purpose can:

Why is it important to be aware of you audience's interests? a. so that you can teach them new information thy didn't know b. so that you can use opposite ideas in order to shock them c. so that you can use the most effective strategy to persuade them d. so that you can pretend to like the same things and get them to trust you