Lacking an invitationOther delegates to the Parliament of Religions in 1893 represented certain groups, but Swami Vivekananda came as an individual. He did not receive a formal invitation as such. He just came on his own. Then he was given a letter of introduction by Professor J.H. Wright, the Professor of Greek at Harvard University. Unfortunately, Swami Vivekananda lost the letter.
Vivekananda was very upset when he lost the letter, but the great Professor said to him, "To ask you, Swami, for your credentials is like asking the sun to state its right to shine." So this is the wonderful compliment that he gave Vivekananda.
Sri Chinmoy, Transfiguration and other stories, Agni Press, 2007