This tradition originates from old times when Buddha stayed in temples during the rainy season to avoid killing insects or harming the growing seeds. It is a period for study, meditation and teaching of new monks. The monks are allowed to go out during the day but they must sleep in the same temple every night during these three months.
Mostly the activities on Wan Khao Phansa are same as those on any other Buddhist holy days. Two main important things presented to monks during Khao Pansa are the candles and garments worn by monks, especifically the bathing robe.