Magha Puja day falls on the fullmoon of the third lunar month, somewhere toward the end of February. "Magha" is the name of a month in the lunar calendar used in ancient India. The word "Puja" means signifies worship. So Magha Puja means the worship in the month of Magha.
The Magha Puja Day is also known as the day of the Four fold Assembly. This was a special assembly which took place at the Bamboo Grove (Veluvana) and contained for extraordinary features, namely:
1- It was the fullmoon day of the month Magha.
2- 1,250 monk disciples assembled to see the Buddha, alll by themselves, without an appointment.
3- All these monks were Arahants who has attained the sixfold superknowledge.
4- All of them are Buddha's direct disciples having been ordained by the Lord himselves.
At the four fold assembly the Buddha gave the monks an important discourse sumerzingthe his teachings into three main principles, namely:
1- not to do evil
2- to do good
3- to purify the mind
These three principles are fundamental in the Buddha-Dharma ( Buddhist Doctrine).
Sabbapapassa Akaranam kusalassa upasampada
sacitta-pariyodapanam etam buddhanasasanam.
Refering from all evil; doing of what is good and cleaning of one's mind; this is the advice of the Enlightened Ones. Dhammapada
Magha Puja Day is also known as the Dharma Day as it was the occasion an important Dharma discourse was delivered by the Buddha.
Magha Puja Day is also important in another respect. It is said that in the last year of his life, jst three months before his passing away, the Buddha had demined the day he would die and announced it to his disciples. The incident is known as the Rejection of of the Aggregates of Life and it also took place on the fullmoon of the third junar month (Magha). This fact adds more significance to the Magha Puja Day and makes it even more sacred for all Buddhists.
On Magha Puja Day, Buddhists flock to the temple in the morning. They observe the five precepts, listen to a sermon, meritorous activities. They also perform circumambulation, walking around the thrine or a Buddha image three times, as a gesture of faith and respect in the Holy Triple Gem.
In the evening Buddhists come to the temple to listen to the monks chant the Paritta. They pay respect to the Triple Gem, observe the five precepts and invite the monks to chant the Paritta to bless them to live in happiness. After listening to the Paritta, they invite the monks to give them the lecture about the origin of this ceremony and tell them how to do good deed.
At night some Buddhists go back home, some Buddhists stay with the monks to recite the rythm of the Dharma verses all night. Some temples the monks change their turns to preach about the the Life of the Buddha also all night.