What Is the Second Moon?

Original text of the Sutra of Perfect Enlightenment: 善男子。一切众生。从无始来。种种颠倒。犹如迷人。四方易处。妄认四大。为自身相。六尘缘影。为自心相。譬彼病目。见空中华。及第二月。 

Explanation: The Buddha said: Good sons, all sentient beings, since beginningless kalpas, have constantly harbored all kinds of inverted views and thoughts in their minds, like a person who has lost his way, wandering in all directions, ceaselessly searching for where he belongs. Lacking wisdom, they groundlessly take the material body composed of the four great elements to be their own body, and take the images of the six sense objects conjured up through grasping to be the appearance of their own minds. They go so far as to become fully convinced and to affirm that the four-element material body is "me" and that the images of the six sense objects are the appearance of their own mind, without the slightest doubt, clinging to them stubbornly until death, and so for beginningless kalpas they have been sinking in the river of birth and death, unable to attain liberation. When the inverted minds of sentient beings perceive these illusory marks, it is just like diseased eyes seeing flowers in the sky, or seeing a second moon. The second moon seen by diseased eyes in fact does not exist—there is only the first moon, the true moon. Likewise, all the dharmas seen by inverted sentient beings do not truly exist; there is only the true suchness of one's own mind. When will sentient beings be cured of their disease, no longer be inverted, no longer recognize false marks, and see only the appearance of the true mind?