Answer: Juliet’s love for Romeo in spite of his family name
Explanation:
Based on the information in the scene, it basically implies that the names given to things or people should not define what those things are or what people are.
The Montagues, are enemies of the family of the Capulets, yet their children fell in love. It's basically saying their names shouldn't define them or change how they feel about each other.
Therefore, the purpose of the speech was to illustrate Juliet’s love for Romeo in spite of his family name.