What do the first moon, the second moon, and the moon's shadow refer to respectively?

(2) Original text of the Śūraṅgama Sūtra, Volume Three: 佛告文殊。及诸大众。十方如来。及大菩萨。于其自住。三摩地中。见与见缘。并所想相。如虚空华。本无所有。此见及缘。元是菩提。妙净明体。云何于中。有是非是。文殊吾今问汝。如汝文殊。更有文殊。是文殊者。为无文殊。如是世尊。我真文殊。无是文殊。何以故。若有是者。则二文殊。然我今日。非无文殊。于中实无是非二相。 

Explanation: The Buddha told Mañjuśrī Bodhisattva and the great assembly: The Tathāgatas of the ten directions and the great bodhisattvas, dwelling in the samādhi of the equal cultivation of Samādhi and Prajñā that they themselves abide in, see that the essence of seeing, the conditions that give rise to the essence of seeing, and the marks conceived in the mind are all like flowers in empty space—originally nonexistent. This essence of seeing and its conditions are originally the wondrous, pure, luminous essence of bodhi. How could there be, within this, distinctions of "is" and "is not"? Mañjuśrī, I now ask you: for example, you, this Mañjuśrī—is there another Mañjuśrī called Mañjuśrī, or is there no other Mañjuśrī? Mañjuśrī Bodhisattva said: It is so, World-Honored One. I am the true Mañjuśrī; there is no other Mañjuśrī called Mañjuśrī. Why? If there were a Mañjuśrī that "is," there would be two Mañjuśrīs. Yet I now am not without Mañjuśrī. Within this, there truly are no two marks of "is" and "is not." 

Original text: 佛言。此见妙明。与诸空尘。亦复如是。本是妙明。无上菩提。净圆真心。妄为色空。及与闻见。如第二月。谁为是月。又谁非月。文殊。但一月真。中间自无。是月非月。是以汝今。观见与尘。种种发明。名为妄想。不能于中。出是非是。由是精真。妙觉明性。故能令汝。出指非指。 

Explanation: The Buddha said: This wondrously luminous essence of seeing and all the empty dusts are also like this. They are originally the wondrously luminous, unsurpassed bodhi, the pure, perfectly luminous true mind, falsely divided into form and space, as well as the seeing, hearing, awareness, and knowing of the six consciousnesses. It is like the second moon—which one is the moon, and which is not the moon? Mañjuśrī, as long as there is one true moon, within the true moon there is originally no distinction of "is the moon" and "is not the moon." Therefore, the essence of seeing and the dust-marks that you now observe, with all their various manifestations and clarifications, are called deluded thinking; you absolutely cannot produce "is" or "is not" from within them. Because of this refined and true mind, the nature of wondrous awakened luminosity, He can enable you to point it out or not point it out. 

Here the Buddha says that the essence of seeing of the seven consciousnesses, the conditions that the essence of seeing perceives as objects, and all the marks conceived in the mind are all like flowers in empty space, originally nonexistent, with nothing at all, because they are originally the tathāgatagarbha, the wondrous, pure, awakened luminous essence of the self-nature of bodhi. How could there still exist within this the distinction of "is" and "is not"? It is just like you, Mañjuśrī Bodhisattva—there is no other Mañjuśrī who could be called "is Mañjuśrī" or "is not Mañjuśrī." The key point the Buddha especially emphasizes is that the conscious mind that sees, the conditions that give rise to seeing, and all the dharmas that are seen are all the true mind of the first moon; there is no second moon or reflected moon, and the second moon and the reflected moon are also the wondrously luminous true self-nature of bodhi. The Buddhas and bodhisattvas of the ten directions all see the true mind of the self-nature of bodhi, and do not see the illusory marks manifested by the true mind. As long as bodhi is true, everything is true; there is no need to distinguish what is true and what is false—the whole is the true suchness, the essence of the one true dharma realm.