How important is the theme of identity to an interpretation of Rudyard Kipling's Kim?
As in much of Kipling, identity is a crucial theme in Kim. Kim's identity as both European and Indian is crucial to the story. He is born the child of Irish parents but raised as an Indian boy on the streets of Lahore after his parents die, his skin baked so dark he can pass as a native. Kim's power derives precisely from his fluid identity and his ability to straddle cultures, that of the British overclass and that of India. If he had been raised merely British, he would have been lacking in some of the skills—such as the ability to pass as Indian—that the British spy service needed to protect the country from the Russians. However, the novel also shows that had he been merely Indian, he would have been unable to resist the "superstitions" and "backwardness" of India, also making it difficult for him to provide what Britain needed. Kipling's point is that a hybrid identity that incorporates strengths from both cultures was crucial to making India strong—of course, in service to the British empire.
Rudyard Kipling's Kim is a novel about a young man caught between two cultures, Indian and British. Although of Irish ancestry, Kim has been raised in India. Being Irish in the nineteenth century was a somewhat fraught identity, given that Ireland, like India, had been conquered by England and many Irish were agitating for independence. In India, Kim is brought up by a half-caste, who is also an outsider, and later attaches himself to a Tibetan. All of these positions are marginal ones, which position Kim as located on the fringes of society, looking in from the margins. This position is precisely what makes him such a potentially good spy.
Thus issues of identity are very much at the center of the novel and should be discussed in any interpretation of it. The most important literary theory you should use in discussing the novel is postcolonial criticism, as it addresses this issue of identity in nations which have been colonized by foreign powers.