Ramakrishna himself explained the meaning of his illness:
Quote:Meaning of His Illness
One evening Shrī Rāmakrishna was attended by his faithful servants Shashi (Rāmakrishnānanda) and Kālī (Abhedānanda), who were waiting upon him. The Bhagavān opened his mouth and inspired them by saying: “The illness of my body is caused by the sins of those who come and touch my feet. I purify the sinners by taking their sins upon myself and suffering for them. He who was Rāma, who was Krishna, Buddha, Christ, and Chaitanya, has now become Rāmakrishna. Blessed are those who know this truth. My Divine Mother has shown me that the photograph of this body will be kept upon altars and be worshipped in different houses as the pictures of other Avatāras are worshipped. My Divine Mother has also shown me that I shall have to come back again and that my next incarnation will be in the West.”