十不二門指要鈔 1.114

1.114

三、此即下，結門所從。十門理一莫不相由，今從依境修觀，內外二境皆色心故。此二妙故，內外不二也。

Third, from "This is..." downward concludes what the gate derives from. The principle of the ten gates is one, and they inevitably derive from one another. Here it proceeds from cultivating contemplation based on the object, because both the internal and external objects are form and mind. Because these two are subtle, internal and external are nondual.