Asalha Puja (in Thailand also called Asanha Bucha) is one of the most important Buddhist festivals and is often held in the form of a puja. It is celebrated on an Uposatha, a day of the full moon in the eighth month (usually corresponding to our July) of the lunisolar calendar.
The festival commemorates the first speech of the Buddha to his followers in the deer park of Sarnath near Varanasi (today Benares) after he had been enlightened.
In this speech all the basic ideas of Buddhism are already found. Here Buddha speaks of the wheel of teaching (Dhamma wheel) and of the four noble truths:
Truth from suffering (Dukkha Sacca). Truth from the cause of suffering (Samudaya Sacca). Truth from the end of suffering (Nirodha Sacca). Truth from the way to the end of suffering (Magga Sacca). The goal of Buddhist teaching is to establish criteria that allow discrimination between right and wrong. Abilities that lead towards this goal are valuable. Abilities and thoughts that lead away from this goal are harmful.
Buddha says in this speech that he had not heard of these truths before. He had become enlightened as "Buddha" by himself. It is only through him that his listeners attain knowledge that can enable later enlightenment.