importance of cleanliness in human life?

Answer 1

There are two aspects to this:
- physical cleanliness;
- cultural or ritual cleanliness;

Physical cleanliness is essential for human existence. By far the most important aspect of physical cleanliness is clean water. It Keeps such diseases as Cholera and Diarrhoea at a distance. These diseases and others like them them are the biggest killers in history.

Cultural or ritual cleanliness is important in many cultures as a marker of status or caste or of belonging to the group. One example is the lower and out caste segments of Indian society that do the cleaning and sanitary functions necessary to the society. Another example is the use of ritually clean food (kosher, halal, etc.) to mark the belonging to a particular group.

There is quite an extensive literature in Anthropology concerning cleanliness and purity. Try a search with those terms (Anthropology, cleanliness, purity).