Meijouseichoku

The concept of purity (meijouseichoku) is central to Shinto. Purity is thought to promote happiness and good fortune, while impurity (kegare) leads to the opposite.

Purity and impurity are not quite the same as good and evil. One might support a bad cause with a pure heart; indeed this would be more admirable that halfheartedly supporting a good cause.

In order to promote purity one should live a simple life in harmony with nature, honor traditions and one’s family, maintain physical cleanliness, and avoid contact with impure people and things. Since this is not always practical, much of Shinto practice is devoted to purification rituals.

Source: http://bugfox.net/fun/2010/09/07/notes-on-the-shinto-religion-and-anime/