It is difficult to cull a satisfying thematic interpretation from Christina Rossetti's "Goblin Market." Obvious themes might be "that one should be careful of temptation," or "that little girls should not talk to strange men." One might even go on to the end of the poem and decide the theme is "that sisters should love one another." These are rather trite ideas, however, and while the poem definitely supports them (and they are easily defended with quotations from the text), a more careful look at "Goblin Market" reveals that the poem is fairly complex, and able to support a more revolutionary reading than the ones put forth above. Rather than saying that "Goblin Market" has a particular theme, I would put forth the notion that it attempts to deal with certain problems Rossetti recognized within the canon of English literature, and specifically with the problem of how to construct a female hero.
There are no signifecant female heros in English literature up to the time of Rossetti. Female protagonists exist, of course, like Elizabeth in Austen's Pride and Prejudice, but they have no outlet for heroic action. They are constrained by the gender-roles into which a male-dominated society has placed them. Elizabeth must spend a good deal of her energy waiting for Darcy to take action; she herself is hobbled by the cords of decorum.
In "Goblin Market," Rossetti creates a rudimentary framework of behavior in which a female hero -- a heroine -- might operate. Rossetti's efforts are to some degree successful, though she fails to solve the problem completely.
Throughout the poem Lizzie remains pure; this is nothing new. The role of the unstained virgin has existed longer than the English language. Spenser's Florimell provides an early example. What is different about Lizzie is that she actively pursues temptation with the intention of conquering it....