According to the layer of the Pali Canon most concerned with making merit, acts of merit are most fruitful when planted in the appropriate “field”: either the Buddha-field surrounding a relic (or, by extension, a Buddha image); or legitimate members of the monastic Sangha. The importance of the Buddha-field explains the cults of stupas, Buddha images, and Buddha amulets that thrive in the Theravadin world. The importance of the monastic Sangha as a field of merit explains the devotional cults surrounding individual monks or nuns who are believed to be noble disciples. [BR, 144]

General familiarity with rituals, both animistic and Brahmanical, has...influenced the typical villager’s view of karma in that merit is often seen as residing, not in the quality of the intention behind an action, but in the proper performances of acts that are defined as meritorious. This view differs radically from the view of kamma as expressed in the earliest layer of Suttas....A prime example of this sort of accomodation is the typical merit-making ritual on the morning of the Uposatha, which occurs on the days of the full, new, and half moons. The primary function of the ritual is to make merit by presenting food to the monks and listening to a sermon. Monks and villagers gather in separate zones of the main meeting hall. The general mood of the gathering is cheerful. Before the food is presented, the villagers pay respect to the Buddha-image and request the Triple Refuge and Five Precepts from the chief monk. For those who have had recourse to animist or Brahmanical practices since the last Uposatha service, and who believe that their allegiance to the Buddha, Dhamma, and Sangha has thus been tarnished, the request for the Triple Refuge offers the chance to renew allegiance with no questions asked. For others, it is an opportunity to renew their sense of prasada [serene confidence that one has found the way] in the Triple Gem. The request for the Five Precepts serves a similar dual function. On one level it is ritualistic: a donation is said to bear the greatest fruit if both the donor and the recipient live by the precepts. For those who have little intention of trying to observe the precepts after leaving the monastery, the act of taking the precepts puts them “in possession of” the precepts at least while the donation is being given. For those who do intend to keep the precepts, the request is an opportunity to renew their dedication and make a fresh start if they have broken any precepts since the last Uposatha. Once the preliminaries are completed, the villagers as a group make a formal declaration of donating their offerings to the Sangha. This is because the act of making a donation to the Sangha is more meritorious than that of donating it to individual monks….Only then is the food formally handed to the monks, who chant blessings rejoicing in the merit the villagers have made. The monks then eat while the villagers look on, chatting informally about the events of the past week. [BR, 162-3]

Wherever Theravada Buddhism has become the dominant religious ideology, it has also tended to coexist with beliefs in indigenous spirits and deities. In part this is due to the Theravada understanding of the Buddha himself: he is a “converter,” he is a “refuge,” but he is not an active “protector.” Though devotees may well turn to him in their soteriological concerns, he has basically transcended this world and does not interfere directly in the mundane concerns of people. Thus, in Sri Lanka and Southeast Asia, the Buddha occupies a position at the top or, perhaps better, “above the top” of a large pantheon of spirits who are concerned with mundane affairs. This pantheon is not always well organized, but it includes regional and local divinities, guardians of towns and villages, spirits of the dead, and demonic and autochtonous forces concerned with illness, fertility, protection, success, failure, and the like.
       The relationship of the worship of these spirits (called nat in Myanmar [Burma], and phi in Thailand and Laos) and the practice of Buddhism has long retained the interest of scholars. Although the situation can be quite complex, Buddhists in these countries do not generally see any contradiction between their veneration of the Buddha and their veneration of these deities. And though rituals toward them may vary (for example, certain indigenous spirits may be offered animal sacrifices or whiskey, while the Buddha and the more buddhaized spirits will receive only cooked food and flowers), often, in festivals, there is a mixture of elements that may baffle Westerners brought up in more exclusively monotheistic traditions. [EB (2nd edition), 219]