起信論疏筆削記 19.47

19.47

今借此意下，三、依法正揀。經中三喻以驗行人真實虛偽，故文云：行人亦爾也。故共事等三試之。今文將以驗於定境，不同經意，故云借此等，但借其喻，非取法也。不淨觀者，隨看當初所修何觀，或數息、或不淨等。今於此禪發其境界，即却依本時修習，即驗邪正也。

From "Now borrowing this intention" onward is the third: correctly discerning according to the Dharma. In the sūtra, the three analogies are used to test whether a practitioner is genuine or false; hence the text says: "Practitioners are also like this." Therefore, one tests them with the three: working together, and so on. Now, the text is going to use them to test the states of concentration, which differs from the sūtra's intention; hence it says "borrowing these," etc., only borrowing its analogies, not taking its method. Regarding the contemplation of impurity: depending on which contemplation one originally practiced—whether mindfulness of breathing, impurity, or the like—now, when a state arises in this dhyāna, one simply returns to cultivating in accordance with one's original practice, and thereby tests whether it is heterodox or orthodox.