Why does Shakespeare choose to introduce macbeth in a conversation with a soldier in act 1 scene 1-2

What does the simile add to the passage

Brendan is playing in the backyard.

Fine fellow, that lebrun," said arobin when robert had gone. "i never heard you speak of him.""i knew him last summer at grand isle," she replied.  what becomes apparent during this conversation? robert and arobin are both aware they are rivals for edna’s affections.arobin is unaware of robert’s role in edna’s life, but robert is aware of arobin’s role.robert is completely unaware of arobin’s romantic intentions and love for edna.robert has much more confidence in himself than arobin does.