I fear that I may debase these passages if I try to interpret them, but I dare do so in order to answer your question. The gist of these passages is that 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 words of myō, hō, ren, ge, and kyō 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.

Kanjin Honzon-shō, A Treatise Revealing the Spiritual Contemplation and the Most Verable One, Writings of Nichiren Shōnin, Doctrine 2, Page 146