The girls in the last post that you saw in YouTube were singing the “Buddha Jaya Mangala Gatha,” or “Chant to the Buddha’s Victories.” This is a very famous chant in Thailand and in other Theravadin countries. As far as I know the verses were composed by a Thai monk in the fifteenth century C.E. and were dedicated to King Naresuan the Great in his campaign for Siamese independence against the Burmese. It is said that the King was so fond of these verses that he requested that the monks chant them every time he went to war. And he was never defeated anywhere in battle.
The content of the verses, however, had absolutely nothing to do with wars. The prayer consists of eight verses, each depicint the Buddha’s victories against his opponents. However, the main thing is that it is the Buddha’s own victory against defilements and the Mara, who is the personification of defilements and everything that is the obstacles against achieving Buddhahood and Nirvana.
In the first verse, the Buddha defeats the Mara during the moment of his achieving Buddhahood. When Siddhartha Gautama was about to become the Awakened One, the Mara came to him together a full army and numerous weapons. The Mara was intent on bringing Gautama down so that he did not become enlightened. However, due to the merits that the bodhisattva had accrued in countless lifetimes in the past, the bodhisattva was able to defeat the Mara and the whole army. This is the most important episode in the whole life history of the Buddha. It shows the moment when an ordinary person actually became ‘Buddha’ or ‘Awakened One.’ All the weapons hurled to the Buddha were transformed into flowers and garlands. The merit that he had accumulated came to help him in form of a torrent of flood washing away the Mara and his army.
The remaining seven verses refer to other episodes of the Buddha’s victories, such as his defeat of the demon Alavaka, Angulimala and others.
The whole point of the chant is to reflect on the life and career of Gautama Buddha so that we ourselves follow his path and become free from all defilements ourselves.