The "love-in-idleness" flower is a flower that has been hit with Cupid's arrow. One night Oberon saw Cupid "[f]lying between the cold moon and the earth" and take aim at a fair young maiden (II.i.158-161). But the arrow missed and landed in a flower instead. Oberon describes that the flower had been "milk-white" but is now "purple with love's wound" (170). Oberon further states that now that the flower has been hit by Cupid's arrow, it now can serve as a love potion. If the flower's juice is squeezed onto the eyelids of a sleeping person, when that person awakes, he or she will fall in love with the first being he or she sees.
Oberon intends to use the flower on his wife for two purposes. The first purpose is to avenge himself on his wife for refusing to give him the Indian boy he is coveting, as we see in his lines, "Well, go thy way; thou shalt not from this grove / Till I torment thee for this injury" (II.i.148-149). However, literary critic Shirley Nelson Garner asserts that their is a deeper reason. Not only is Oberon jealous of the boy, Oberon is jealous of Titania's affection for the boy. Oberon wants all of Titania's affection all to himself and sees the boy as an impediment. It is evident that Titania is feeling somewhat of an erotic affection for the boy, as we see her crown the beautiful Indian boy with flowers and make him "all her joy," which is exactly how we see her treat Bottom when she falls in love with him (27). Hence, Oberon is planning to use a love potion to distract Titania into falling in love with something other than the boy so that he can trick her into releasing the boy, thereby removing what Oberon sees as an impediment in their relationship. Once Titania gives up the boy, Oberon will once again have his wife's affection all to himself.