It is the “wide” practice to uphold, read, recite, and defend with delight the total of the Lotus Sūtra consisting of 28 chapters in 8 fascicles. It is the “abbreviated” practice to uphold and keep the important chapters such as the “Expedients” and “The Life Span of the Buddha” of the Lotus Sūtra. It is the “essential” practice to chant only the four-phrase verse of “The Divine Powers” chapter* or the daimoku or to protect those who do so. Of these three kinds of practices to chant only the daimoku devotedly is the essence of the essential.
Hokke Daimoku Shō, Treatise on the Daimoku of the Lotus Sūtra, Writings of Nichiren Shōnin, Faith and Practice, Volume 4, Page 39
*The “four-phrase verse of ‘The Divine Powers’ chapter” (shiku yōbō 四句要法) is:
如来一切所有之法。Nyo rai is’ sai sho u shi hō.
如来一切自在神力。Nyo rai is’ sai ji zai jin riki.
如来一切秘要之蔵。Nyo rai is’ sai hi yō shi zō.
如来一切甚深之事。Nyo rai is’ sai jin jin shi ji.
Murano translates this as:
All the teachings of the Tathāgata
All the unhindered, supernatural powers of the Tathāgata
All the treasury of hidden core of the Tathāgata
All the profound achievements of the Tathāgata
(You can find it on p.294 of the 2nd edition)
The verse explains how profound and meritorious the Lotus Sūtra is, saying that all of the above are expounded clearly and revealed in this sūtra.
It is also referred to as “ketchō fuzoku” ( 結要付属 ) – meaning the essence of the Lotus Sūtra which was transmitted to Bodhisattva Superior Practice and other Bodhisattvas from Underground.
This explanation provided by Kanse Capon.