What does Romeo mean by the line "lady, by yonder blessed moon that tips with silver all these fruit-tree tops"? What is shakespeare trying to show...

In ActII sc.2 Romeo who has now become infatuated with Juliet  risks his life by climbing a high wall and jumping into the orchard of the Capulet's home. It is late in the night, the moon is shining dimly and both of them can't see one another.

Unaware of Romeo's presence in the orchard Juliet leans out of the balcony window and confesses her love for him and asks him to:"Deny thy father and refuse his name/Or, if thou wilt not,be but sworn my love/And I'll no longer be a Capulet." Romeo at once replies that he would willingly change his name:"Call me but love and I'll be new baptized/Henceforth I never will be Romeo."

After she has recognised Romeo's voice and identified him- although both are not able to see one another -she asks him,"O gentle Romeo/If thou dost love, pronounce it faithfully." Atonce, Romeo swears that he loves her:"Lady by blessed moon I swear/That tips with silver all these fruit-tree tops..."

Romeo swears on the moon that he loves Juliet. Romeo names the moon as a witness when he pledges his love for Juliet.

 Shakespeare's  plays were performed in the daytime.  Hence, in order to create the scenic atmosphere of night time Shakespeare has to rely on the magic of his poetry. Shakespeare skilfully  uses words to create an intensely dark night dimly lit up by the moon:"the envious moon/Who is already sick and pale with grief."