Christina Rosetti’s Goblin Market chronicles two girls, young maidens Laura and Lizzie, who come across a market of goblins as they walk through the woods. The goblins symbolize strange men, who cannot be trusted, yet still Laura, the more naive one of the two, is drawn to them for the items they sell.
Lizzie warns Laura repeatedly to not give into her temptations, but alas she approaches the goblin men. She says “Good folk, I have no coin; … they answered all together ‘buy from us with a golden curl'”, cuts a piece of her hair off and receives the various fruits they are selling. After this, she begins longing for the fruits again and again.
Lizzie warns her again that “‘dear, you should not stay so late, twilight is not good for maidens; should not loiter in the glen, in the haunts of goblin men. Do you not remember Jeanie, how she met them in the moonlight, took their gifts… but ever in the noonlight she pined and pined away… found them no more, but dwindled and grew grey; then fell with the first snow, while to this day no grass will grow where she lies low.'”
This symbolizes what pleasure can do to the human brain, and that once something “good” is given to someone again and again, it becomes hard not to pine and long after it when it is taken away. The theme is just that, longing.
This sense of longing is very accurate to what is portrayed in the poem. Although a focus that you could also put is the looks of the goblin men. They are an inhuman creepy sort of lot, and even despite all of that, Laura still yearns for the fruit. This could also play into a self destructive nature kind of reading. Where people (in this case Laura) forgoes the looks of things for self satisfaction.