起信論疏筆削記 18.22

18.22

標數中，疏　四不壞信者，信彼四事皆不可壞，不壞即常住也。以所信之境不可壞故，使能信之心亦不可壞。能所相稱，俱名不壞，故經云：妙信常住是也。

In stating the number: [Commentary:] "Four indestructible faiths" means placing faith in those four matters as all being indestructible; indestructible means eternally abiding. Because the objects of faith are indestructible, they cause the mind that has faith to also be indestructible. Subject and object correspond to each other, and both are called indestructible. Thus a sūtra says: "Wondrous faith is eternally abiding"; this is it.