大方廣圓覺修多羅了義經略疏 2.972

2.972

三也。城喻覺者，法、喻各有三義：一、了心性空，眾惑不入，如防外敵；二、見恒沙德則萬行圓增，如養人眾；三、道無不通，如開門引攝。

This is the third. Comparing enlightenment to a citadel has three meanings in both the doctrine and the metaphor: first, realizing that the mind's nature is empty, the defilements do not enter, like defending against external enemies; second, seeing virtues numerous as the sands of the Ganges, the myriad practices fully increase, like nurturing the populace; third, the Path is unimpeded everywhere, like opening the gates to draw in and gather.