Chanting the daimoku is the heart and core of the entire sutra

Moreover, I chant the daimoku, which is the heart and core of the entire sutra, and I urge others to do likewise. Although the mugwort growing in a hemp field or wood marked for cutting with an inked line may not be straight to begin with, they will as a matter of course become so. In the same way, one who chants the daimoku as the Lotus Sutra teaches will never have a twisted mind. For one should know that, unless the mind of the Buddha enters into our bodies, we cannot in fact chant the daimoku. 25/10

The Writings of Nichiren Daishonin
The Blessings of the Lotus Sutra
Written to Myomitsu on March 5, 1276