why does gatsby tell nick about his life

Gatsby invites Nick to lunch in the city. He proudly displays his Rolls-Royce, then abruptly asks Nick what he thinks of him. Nick is understandably evasive. Gatsby responds to his reticence by giving Nick an account of his past. His story, however, is highly improbable. Though he claims to descend from a prominent Midwestern family, when Nick asks him which Midwestern city he comes from, Gatsby hesitates, then says "San Francisco." He rattles off an absurdly long list of accomplishments: he claims to have studied at Oxford and lived in all of the capitals of Europe; then he enlisted in the war effort, where he was rapidly promoted to major and decorated by every Allied government, including Montenegro. He pulls out a photograph of himself in Oxford cricket whites, as well as a medal awarded by the government of Montenegro, in order to corroborate his story. Gatsby's ultimate motive is to gain Nick's help with Daisy.