What does the phrase "teach the torches to burn bright" suggest in Romeo and Juliet?
Juliet is so beautiful that even torches are not as bright as she.
This quote is from this line when Romeo first sees Juliet, before he knows who she is.
O, she doth teach the torches to burn bright! (Act 1, Scene 5)
Basically, with this line Romeo is saying that Juliet is so beautiful that her beauty is brighter than a torch. She is so bright, that the torches learn to be bright from her. It is another metaphor on Juliet's beauty.
Romeo is infatuated by Juliet’s beauty and, blinded by her beauty, has not really stopped to consider anything else. Romeo goes on and on with many beautiful lines about Juliet’s looks, but never once does he mention her personality. He compares her to the sun, and a jewel, and says in this line that the torches get their light from her. However, he is not talking about her glowing personality. He is again talking about her looks.
Beauty too rich for use, for earth too dear!
So shows a snowy dove trooping with crows,
As yonder lady o'er her fellows shows. (Act 1, Scene 5)
Romeo proposes soon after. Romeo has only just met Juliet, and he didn’t even have a real conversation with her. They share a cute conversation that was all in metaphors. What is she like? Does she like roses? Is she allergic to strawberries? What does she do on weekends? He has no idea! He has spent no time with this girl. He just took one look at her and fell head over heels in love with her.