大乘百法明門論開宗義決 1.143

1.143

慚等雖善非淨為相等者。此通外難。謂有難言。若說心淨名為信者。若淨即心應非心所。若令心淨慚等何別。慚等亦能令心淨故。如何唯說心淨名信。為通此難故有此文。

Regarding "although shame and the like are virtuous, they do not have purity as their characteristic": this resolves an external objection. That is, someone objects: "If one says that purity of mind is called faith, then if it is purity itself, it should be the mind and not a mental factor. If it causes the mind to be pure, how does it differ from shame and the like? Since shame and the like can also make the mind pure, why is it that only purity of mind is called faith?" It is to resolve this objection that this passage exists.