What we should chant all the time as the practice of the perfect teaching is “Namu Myōhō Renge Kyō,” and what we should keep in mind is the way of meditation based on the truth of “3,000 existences contained in one thought.” Only wise men practice both chanting “Namu Myōhō Renge Kyō” and meditating on the truth of “3,000 existences contained in one thought.” Lay followers of Japan today should recite only “Namu Myōhō Renge Kyō.” As the name has the virtue of reaching the body for which it stands, when one chants “Namu Myōhō Renge Kyō” one will not fail to receive all the merit of the Lotus Sūtra.

Jisshō-shō, A Treatise on the Ten Chapters of the Great Concentration and Insight, Writings of Nichiren Shōnin, Doctrine 2, Page 4