"Pray you sir, a word. And, as I told you, my young lady bid me to inquire you out. what she bid me say, I will keep to myself."(II.IV.165-168)
Romeo and the NurseThe Streets of Verona (Noon)
"But first let me tell you, if you should lead her in a fool's paradise, as they say, it were a gross behavior, as they say."(II.IV.168-170)
The Nurse threatens Romeo about what would happen if he ever broke Juliet's heart. (Revenge)
"Nurse, commend me to thy lady and mistress. I protest unto thee-"(II.IV.175-176)
For the gentlewoman is young; and therefore, if you should deal double with her, truly it were an ill thing offered to any gentlewoman, and very weak dealing."(II.IV.170-174)
This relates to the motif of revenge, because although no action is actually taking place, the Nurse is threatening to enact revenge for the suffering of a loved one, Juliet.
Shakespeare is correlating the motif of revenge with the theme of love. He shows that revenge is not only caused by personal suffering, but also the suffering of loved ones. He shows through the Nurse the things one does when the ones they care about gets hurt.
The Nurse is the perfect character to express motifs and themes through. Because of her unrelated tangents and long speeches, she can express the themes Shakespeare desires to be shown without it seeming like beyond her character traits.