The (Underlying) Nature of Perception is Not the Essence of Perception
Ananda asked: I now understand that the nature of Perception annot be returned to any external cause but how can I
know that it is my True Nature?
The capacity of perception
The Buddha said: Ananda, though you have not yet reached the state beyond the stream of transmigration, you may now use the Buddha's transcendent power to behold the first dhy‡na heaven without obstruction, like Aniruddha who sees this world (Jambudvipa) as clearly as fruit held in his own hand. Bodhisattvas can see hundreds and thousands of worlds. Buddhas in the ten directions can see all the Pure Lands as countless as the dust. As to living beings, their range of sight is (sometimes) limited to inches.
Picking out causal objects
Ananda, as you and I see the palaces inhabited by the four heavenly kings with all that is there in water, on the ground and in the air, though there is a great variety of forms and shapes in the light and darkness, they are but hindrances resulting from your differentiation of objective phenomena.
Here you should distinguish between your own Self and external objects. From, what you see, I now pick out that which is your own Self and those which are but phenomena.
Ananda, if you exhaust the field of your vision, from the sun and moon to the seven mountain ranges with all kinds of light, all that you see are phenomena which are not YOU. As you (shorten your range) you see passing clouds and flying birds, the wind rising and dust, trees, mountains, rivers, grass, men and animals; they are all external and are not YOU.
The essence of perception
Ananda, the great variety of things, far and near, when beheld by the essence of your seeing, appeared different whereas the nature of your seeing is uniform. This wondrous bright essence is really the nature of your perception.