Not everything is a mantra! (as sometimes presented in 'mantra' concerts in the west). Mantra has a very specific definition and certain elements have to be present for a text to be called mantra. So not all text from India are mantra: there is mantra, then there is a kirtan, then there is a bhajan, there are ‘pads’, ‘chopais’ ‘chalisas’ ’stutis’, ’stotras', then there are shabads... and many more forms and styles. For something to be a mantra, it has very clear requisites, but one has to learn these from the right source to know the difference.
The so called "kundalini mantras" sung mainly in USA, they are not mantras: they are sacred texts from holy book GURU GRANTHSAHIB but not mantra - this is just an American creation and a big 'enterprise' - actually Sikhs from India don’t even believe in mantra, they never sing mantras, they just recite and sing the sacred texts and songs of Nanak and other Sikh Gurus. If you say to a Sikh that Wahe Guru Wahe Jio is a mantra, he may be actually offended. Mantras were only accepted in Buddhist and Jaina tradition apart from Sanatan Dharma (known as Hinduism). Kundalini Mantras are only present in the Western Sikhism started by Yogi Bhajan. Before that, there is no record of Sikhs chanting mantras. And Western Sikhism (or Kundalini Sikhism) has nothing much to do with the actual Sikhism. Sikhs do not do yoga, sikhs do not chant mantras - as simple as that. In fact there is nothing like Kundalini Yoga, which was taught by Yogi Bhajan, in the whole history of Indian Yogic Science.
So for example, let's tals about a Bhajan. A BHAJAN is any type of Hindu Devotional Song that to human ears is heavenly. And if it's purely devotional, it's truly divine. Such a genre of music is the bhajan.
Nothing can be more deeply rooted in the Indian tradition than bhajans. Bhajans are simple songs in soulful language expressing the many-splendored emotions of love for God, a complete submission or self-surrender to him through singing.The medieval age saw devotees like Tulsidas, Surdas, Meera Bai, Kabir and others composing Bhajans.
The words, tunes, rhythms and the typical repetitive style of the bhajans give a certain sense of permanency that is known as shashwat (freedom from the state of flux), something each one of us is secretly pining for.
In Hinduism, Bhajan and its Bhakti analog Kirtan, have roots in the ancient metric and musical traditions of the Vedic era, particularly the Samaveda. The Samaveda samhita is not meant to be read as a text, it is like a musical score sheet that must be heard.
Some Bhajan songs are centuries old, popular on a pan-regional basis, passed down as a community tradition, while others newly composed. Everyone in Hindu tradition is free to compose a Bhajan with whatever ideas or in praise of any deity of their wish, but since they are sung, they typically follow meters of classical Indian music, the raga and the tala to go with the musical instruments. They are sung in open air, inside temples such as those of Swaminarayan movement, in Vaishnava monasteries, during festivals or special events, and at pilgrimage centers.
A Bhajan is closely related to Kirtan, with both sharing common aims, subjects, musical themes and being devotional performance arts. A Bhajan is more free in form, and can be singular melody that is performed by a single singer with or without one and more musical instruments. Kirtan, in contrast, differs in being a more structured team performance, typically with a call and response musical structure, similar to an intimate conversation or gentle sharing of ideas, and it includes two or more musical instruments.
Many Kirtan are structured for more audience participation, where the singer calls a spiritual chant, a hymn, a mantra or a theme, the audience then responds back by repeating the chant or by chanting back a reply of their shared beliefs.
A Bhajan, in contrast, is either experienced in silence or a "sing along". The well-known song "Tumi Bhaja re Mana" is an example of a Bhajan.