What does "you may tread me in the very dirt /but like dust, i'll rise?

A figure of speech is any verbal device used to emphasize something. A simile emphasizes a similarity by saying it: "I am like dust: I will rise." Any time you see the word "like" or "as", you have a simile. A metaphor emphasizes a similarity by saying two things are the same. "I am dust: I will rise." A hypocatastasis emphasizes a similarity by calling one thing by the other's name, such as "the serpent" in Genesis.

Your example can also be called "flowery phraseology," since the speaker is not actually inviting anybody to trample him.