"Well, in that hit you miss. She'll not be hit with Cupid's arrow. She hath Dian's wit, and, in strong proof of chasity well armed, from love's weak childish bow she lives unharmed." What is the meaning?

In this scene, Romeo is complaining about how Rosaline does not love him. Romeo's love is unrequited. Romeo says that Rosaline is too smart to be pierced by Cupid's arrow hence she won't fall in love with him. Diana was the goddess of both hunting and childbirth. Ironically she was a sworn virgin.