From the SGI-USA.org website:
Is chanting a form of meditation or is it positive thinking?
Nichiren Daishonin teaches: “A mind now clouded by the illusions of the innate darkness of life is like a tarnished mirror, but when polished, it is sure to become like a clear mirror, reflecting the essential nature of phenomena and the true aspect of reality. Arouse deep faith, and diligently polish your mirror day and night. How should you polish it? Only by chanting Nam-myoho-renge-kyo” (The Writings of Nichiren Daishonin, vol. 1, p. 4).
This passage expresses the main difference between chanting and meditation or positive thinking. Although meditation and positive thinking are valuable for many people, these practices are centered on the mind — calming it and training it — and cannot express the fundamental element of our lives, the highest condition of our lives.
Nichiren Buddhism posits that the Buddhahood inside us far transcends the power of our minds. It is the power of life itself that we tap into to transform our entire lives.
Our thinking does become more positive as a result of chanting, but this is because chanting draws out Buddhahood from the depths of our lives, which naturally changes our ways of thinking. The emergence of Buddhahood becomes the positive basis of every aspect of our lives, including mental and physical.
Chanting is neither traditional meditation, nor positive thinking, though it reaps the benefits of both these practices and much more. The essence of chanting Nam-myoho-renge-kyo is that in the very act of doing so we are expressing our Buddha nature.
Many people associate Buddhist religious practice with silent, interior meditation. But the practice of vocalizing, reciting and chanting various teachings has played a vitally important role in the history of Buddhism. Nichiren’s practice of chanting Nam-myoho-renge-kyo encompasses both. Rather than simply exploring and withdrawing into the private realms of the inner life, our religious practice is focused on bringing forth our highest inner potential in relation to and for the benefit of our fellow humans and human society. Nichiren often quotes the words of an earlier Buddhist philosopher that "The voice does the Buddha's work."
The essence of chanting Nam-myoho-renge-kyo is expressing our Buddha nature. It is the essential way to reveal our Buddhahood.
xoxoxox
.