The purpose of this speech is to illustrate Juliet’s love for Romeo in spite of his family name.
In these lines she talks about the meaning of names. She says that names should not and do not define what something is. She uses the rose for comparison. A rose could be named skunk or bicycle. However, changing the name does not change the actual rose. It will still smell sweet and be beautiful. She says that she would love Romeo no matter what his name was.