Explanation

Abu Ramthah was a physician. When he saw the mark of prophet-hood protruding between the shoulder blades of the Prophet (may Allah's peace and blessings be upon him), he thought that it was a lump formed by waste substances. So, he asked the Prophet (may Allah's peace and blessings be upon him) to let him treat it because he was a physician. The Prophet (may Allah's peace and blessings be upon him) replied that Allah is the Physician, i.e. he is the true healer who treats the disease with the medicine that cures it. His words: “You are only a kind man” mean that you are only kind and gentle to the patient. That is because a physician is the one who is knowledgeable of the true nature of the disease and medicine, and he is the one who is able to grant health and recovery. No one could do this but Allah.