It has been said that: “In this (the Dharma Ending) age, the Dharma will disappear. The first Sutra to disappear will be the Shurangama Sutra. That is why those who study the Buddhadharma should first investigate the Shurangama Sutra. As long as someone understands this Sutra, the Buddhadharma will not become extinct.”
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Furthermore, “As long as there is someone who can recite the Shurangama mantra (which is part of the Sutra), the demon-kings, the heavenly demons and followers of externalist teachings will not dare to come into the world to play their tricks and to make trouble. The Shurangama Mantra is the most miraculous mantra for helping the world. The Shurangama Sutra is the primary Sutra which protects and supports the Orthodox Dharma.” — Ronald B. Epstein, Ph.D
An excerpt from this sutra:
The Buddha told Ananda, “You constantly hear me explain in the Vinaya that there are three unalterable aspects to cultivation. That is, collecting one’s thoughts constitutes the precepts; from the precepts comes samadhi; and out of samadhi arises wisdom. Samadhi arises from precepts, and wisdom is revealed out of samadhi. These are called the Three Non-Outflow Studies.”
“Ananda, why do I call collecting one’s thoughts the precepts? If living beings in the six paths of any mundane world had no thoughts of lust, they would not have to follow a continual succession of births and deaths.
“Your basic purpose in cultivating is to transcend the wearisome defilements. But if you don’t renounce your lustful thoughts, you will not be able to get out of the dust.
“Even though one may have some wisdom and the manifestation of Chan samadhi, one is certain to enter demonic paths if one does not cut off lust. At best, one will be a demon king; on the average, one will be in the retinue of demons; at the lowest level, one will be a female demon.
“These demons have their groups of disciples. Each says of himself that he has accomplished the Unsurpassed Way.
“After my extinction, in the Dharma-ending Age, these hordes of demons will abound, spreading like wildfire as they openly practice greed and lust. Claiming to be good knowing advisors, they will cause living beings to fall into the pit of love and views and lose the way to Bodhi.
“When you teach people in the world to cultivate samadhi, they must first of all sever the mind of lust. This is the first clear and unalterable instruction on purity given by the Thus Come Ones and the Buddhas of the past, World Honored Ones.
“Therefore, Ananda, if cultivators of Chan samadhi do not cut off lust, they will be like someone who cooks sand in the hope of getting rice. After hundreds of thousands of aeons, it will still be just hot sand. Why? It wasn’t rice to begin with; it was only sand.
“If you seek the Buddha’s wonderful fruition and still have physical lust, then even if you attain a wonderful awakening, it will be based in lust. With lust at the source, you will revolve in the three paths and not be able to get out. Which road will you take to cultivate and be certified to the Thus Come One’s Nirvana?
“You must cut off the lust which is intrinsic in both body and mind. Then get rid of even the aspect of cutting it off. At that point you have some hope of attaining the Buddha’s Bodhi.
“What I have said here is the Buddha’s teaching. Any explanation counter to it is the teaching of Papiyan.
The Tripitaka Master Venerable Hsuan Hua says:
“In Buddhism all the sutras are very important, but the Sūrangama Sūtra is most important. Wherever the Sūrangama Sūtra is, the Proper Dharma abides in the world. When the Sūrangama Sūtra is gone, that is a sign of the Dharma Ending Age. In the Extinction of the Dharma Sutra it says that in the Dharma Ending Age, the Sūrangama Sūtra will become extinct first. Then gradually the other sutras will also become extinct. The Sūrangama Sūtra is the true body of the Buddha; the sarīra (relics) of the Buddha; the stūpa of the Buddha.”