Concepts of purity are important aspects of many different religions. The purity might be physical, spiritual, or both.
Jews, for example, traditionally have a complex set of laws to ensure ritual purity. This includes the forbidding of eating certain animals. Husbands and wives sleep separately while the woman is menstruating, and she takes a ritual bath before rejoining her husband.
Catholics have traditionally had a whole list of things that couldn't be done a day before taking communion, including engaging in sex. In addition, confession was generally required before communion, so that the polluting weight of sins committed could be forgiven.
Religious ritual is something outside and above the every day. This is one of the reasons why issues of purity or corruption can be so fundamental: it is disrespectful to bring pollution into sacred ritual. Temples and churches are often considered sacred space, metaphysically separate from the mundane world. Many neopagans, who don't tend to have permanent sacred spaces, often go through cleansing rituals to prepare a site before sacred work is engaged.
The dead are a considerable source of corruption in Zoroastrianism. The religion sees the world as a combat field for order and chaos, and the decay of death is a definite manifestation of chaos and thus of pollution.
As such, only certain people are even allowed to touch a dead body, and they then have to submit to purification rituals. Rooms in which a body has been are also ritually cleansed.
The month of Ala on the Badi calendar for the Baha'i is the final month of the year and a time for fasting and prayer. The fast is meant to encourage believers to turn away from material and mundane distractions and embrace a more spiritual life. The fast of Ramadan in Islam has a similar purpose.
In addition, the five days previous to Ala are a time for preparatory spiritual purification such as through charity work.
Ala ends with a new year celebration known as Naw Ruz. Thus, believers have shed aside some of the baggage of the previous year in preparation of the new one.