Nichiren Shōnin stated in Kanjin Honzon Shō,

Śākyamuni Buddha’s merit of practicing the Bodhisattva way leading to Buddhahood, as well as that of preaching and saving all living beings since His attainment of Buddhahood are altogether contained in the five characters of Myo, Ho, Ren, Ge and Kyo and that consequently, when we uphold the five words, the merits which He accumulated before and after His attainment of Buddhahood are naturally transferred to us.”
(WNS2, p. 146)

These two merits are called Ingyō and Katoku.