大般涅槃經義記 4.152

4.152

「如良醫」下答上云何處惱不染。如醫療病，不為病污。醫師療病，若不除愈，污其醫道，差則不污。經法如是，若不能治眾生煩惱，污經勢力；除則不污。此明經法資人滅惑。

From "Like a skilled physician..." downward answers the earlier question, "How is one situated among afflictions without being defiled?" Just as a physician treats an illness without being defiled by the illness. When a physician treats an illness, if it is not eliminated and cured, it defiles his medical art; if it is cured, he is not defiled. The scriptural Dharma is likewise: if it cannot treat the afflictions of sentient beings, the power of the scripture is defiled; if it eliminates them, it is not defiled. This explains that the scriptural Dharma assists people in eradicating delusions.