Of the people who put faith in the Lotus Sūtra today, some have faith like fire while others have it like water. Those who have faith like fire refer to those who become enthusiastic upon listening to the preaching but their passion cools down as times goes by, and eventually forget the teaching. On the other hand, those whose faith is like water mean those whose faith is like a ceaselessly flowing water, namely those who retain their faith without retreating.

Ueno-dono Gohenji, A Reply to Lord Ueno, Writings of Nichiren Shōnin, Faith and Practice, Volume 4, Page 126