O blessed, blessed night! I am afeard,Being in night, all this is but a dream, (II.2.139-140)
"Then window, let day in, and let life out," (III.5.41).
Shuts up his windows, locks fair daylight out, and makes himself an artificial night, (I.1.129)
And he will make the face of heaven so fine / That all the world will be in love with night, / And pay no worship to the garish sun" (III.2.22-25).
When Juliet is with Romeo she feels free, and forever alive, yet when daylight shines through her window, the harsh realities of their forbidden love is what they have to face.
This quote creates an emotion and tone for the scene. Romeo is compared to darkness. He is mysterious, and hides from the light most of the time. Romeo is depressed since Rosaline doesn't love him back, and due to this emotion, readers are able to see how hard it is for Romeo to come to terms with reality instead of fantasy.
In this quote, Juliet is saying how Romeo will light up the dark skies, as Romeo lights up her own world. This forbidden love that Romeo and Juliet share, opens up their true identities since readers see how passionate they are about each other, and how they will do anything in order to save each other. Through this, Shakespeare is demonstrating that forbidden love, can carry out oneś true self.