观自然之道，无所观也。不观之以目而观之以心，
Observing the natural Dao, there is nothing to observe. Don’t use the eyes to look, use the heart.
心深微而无所见，故能照自然之性，唯深微而能照，其斯之谓阴。
The heart is deep and subtle and cannot be seen.
If you can see the natural mind, only then can you illuminate the deep subtlety. This is why it is called “yin.”
执自然之行，无所执也，不执之以手而执之以机，机变通而无所系，故能契自然之理，其斯之谓符。
Grasping the movement of nature there is nothing to grasp. Do not grasp with the hand, grasp its nature. Its nature changes constantly and has nothing to restrain it. If one can agree with nature, this is called “fu.”(sealing).
照之以心，契之以机，而阴符之义尽矣。
Illuminate with the mind, agree with its nature and the yin seal is already complete.
李筌以阴为暗，以符为合，以此文为序首，何昧之至也？
Li Quan believed that yin was the dark, using these words to lead the text, how could anyone be completely unclear? – zhang guo commentary of the first passage of yin fu jing