was compiled by the Maha Theras, the teachers of yore (paranakacariya), of Sri Lanka, and today it is known among the Buddhists of Sri Lanka as the Pirit Potha The Book of Protection.
It is customary for Buddhist monks, when they are invited to the homes of the laity on occasions of domestic importance, such as birth days, house-warming, illness, and similar events, to recite the three popular discourses mentioned above. In the domestic and social life of the people of Sri Lanka pirit ceremony is of great significance. No festival or function, religious or social, is complete without the recital of the paritta. On special occasions monks are invited to recite the paritta suttas not for short periods but right through the night or for three or seven days, and at times, for weeks. On such occasions a pavilion (pirit mandapaya) is constructed for the purpose of accommodating the monks at the recital. Before the commencement of the recital the laity present at the ceremony makes a formal invitation to the monks by reciting in Pali three stanzas which explain the purpose of the recital. Then the monks, generally about twelve or fourteen, who have been invited, will recite the three popular suttas. Thereafter a pair of monks will commence reciting the remaining suttas for two hours. They will then retire and will be followed by another pair for another two hours. Two monks must be constantly officiating. In this manner the recital will last till dawn.
While the recital continues there will be found a pot of water placed on a table before the monks. On this table there is also a sacred thread (pirit nula). For an all night pirit ceremony the casket containing a relic of the Buddha, and the Pirit Potha or The Book of Protection written on ola leaves, are also brought into the pavilion. The relic represents the Buddha, the "Pirit Potha" represents the Dhamma or the teachings of the Buddha, and the reciting Bhikkhu-Sangha represent the Ariya-Sangha, the arahant disciples of the Buddha.
The thread is drawn round the interior of the pavilion, and its end twisted round the casket, the neck of the pot of water, and tied to the cord of the ola-leaf book. While the special discourses are being recited the monks hold the thread. The purpose is to maintain an unbroken communication from the water to the relic, to the Pirit Potha and to the officiating monks, (Buddha, Dhamma, Sangha, the Ti-ratana, the three jewels.) A ball of thread connected to "The Three Jewels" and the water, is unloosened and passed on to the listeners (seated on the ground on mats), who hold the thread while the recital goes on.
When the recital in Pali of the entire book is over at dawn, the thread sanctified by the recital is divided into pieces and distributed among the devotees to be tied round their wrists or necks. At the same time the sanctified water is sprinkled on all, who even drink a little of it and sprinkle it on their heads. These are to be regarded as symbols of the protective power of the paritta that was recited. It is a service of inducing blessings. It has its psychological effects.
from the book of protection