That quote argues that the names (labels) that humans give to things are arbitrary and have no bearing on the thing itself.
So if a rose were called something else - had a different label - it would still have the same characteristics, one of which being a sweet smell.
It links to the play because the issue between Romeo and Juliet was that they came from families that hated each other, so they couldn't be together because of their family name. Wrong in my opinion as it's not just about the name, it's about family history which would be the same no matter what their names were.