Offering prayers based on the Mystic Law—chanting Nam-myoho-renge-kyo—is the best and truest offering we can make for the deceased. Because the Mystic Law has the power to help all people attain Buddhahood, not only those here in the present but throughout the three existences of past, present, and future.

From The Wisdom for Creating Happiness and Peace, part 1, revised edition, p. 342