Although there is no difference between the Lords pastimes of appearance and disappearance, the devotees of the Lord do not generally discuss the subject matter of His disappearance. Vidura inquired indirectly from Uddhava about the incident of the Lords disappearance by asking him to relate krsna-katha, or topics on the history of Lord Krsna. Thus Uddhava began the topics from the very beginning of His appearance as the son of Vasudeva and Devaki in the prison of Kamsa, the King of the Bhojas, at Mathura. The Lord has no business in this world, but when He is so requested by devotees like Brahma, He descends on the earth for the welfare of the entire universe. This is stated in Bhagavad-gita (4.8): paritranaya sadhunam vinasaya ca duskrtam/ dharma-samsthapanarthaya sambhavami yuge yuge.