Boon Khao Kam (บุญเข้ากรรม) is Month #1 of Heet Sip-Song – The Twelve Isan Merit-Making Traditions.
Boon Khao Kam is a period of self-purification for Thai monks who broke serious monastic rules. Formally known as pariwatkam (khao means "enter," so Khao Kam means to "join a pariwatkam assembly"), it's a chance to confess these transgressions to an assembly of monks and do penance. Boon Khao Kam is specifically for failures of the thirteen rules (including no deliberate discharge of semen, soliciting sex, making unfounded accusations against other monks in order to get them disrobed, and attempting to create disharmony in the community of monks) of the second-most serious rule group, the sanghadisesa, which require approval from a specially convened group of monks to be absolved. Offenders spend time in symbolic solitude (long ago it would have been genuine solitude, somewhere out in a forest), typically for ten days. Transgressions of other rules, such as lying, eating between noon and dawn, and killing an animal, are handled at a monk's own temple.
Even a minute lapse of rules must be confessed and atoned for. Monks and novices are sometimes told the story of a monk who, while riding in a boat, put his hand in the Ganges River and unintentionally tore a leaf off a plant; or broke off a piece of moss or algae, depending on the storyteller. Year after year he remembered and regretted doing this, but never confessed it because it was such a small thing. As a result, in his next earthly life he was born as a naga.
Few temples host Boon Khao Kam, so monks will usually travel to a temple other than their own to join in with many other monks. However, not every monk joining a pariwatkam assembly has lapsed. Some because the retreat experience provides a chance to make merit or focus their minds. As Phra Apichat of Wat Non Ta Then in Amphoe Non Daeng, Nakhon Ratchasima explained: "It's like taking a shower. Sometimes you take a shower because you are dirty; sometimes you take a shower because it feels good."
Lay people believe that during this time they will earn extra merit for their offerings because the monks are sure to be highly disciplined, and also because there are so many of them. People bring (or donate) food to the temple in the morning – monks cannot leave the temple during Boon Khao Kam, so they do not go out to collect alms as they normally would – and they might also provide drinks for the afternoon. Since the monks are committing themselves to purity, Boon Khao Kam is a good chance for lay people to renew their own commitment to making merit and living a mindful life.
Boon Khao Kam has no fixed date and can occur in December, January, or February regardless of when the first lunar month is. This is the one boon that is no longer widely practiced and many monks do not do it, though the temples that host Boon Khao Gam and the monks that join it still get strong support from the lay community.