Yogācārabhūmi Śāstra, Volume 34 (84)

Original text:问。何因缘故。此三摩地名金刚喻。答。譬如金刚。望余一切末尼真珠。琉璃螺贝璧玉。珊瑚等诸珍宝。最为坚固。能穿能坏所余宝物。非余宝物所能穿坏。如是此三摩地。于诸有学三摩地中。最上最胜最为坚固。能坏一切所有烦恼。非上烦恼所能蔽伏。是故此三摩地名金刚喻。

Explanation: Question: For what reason is this samādhi named with the metaphor of a vajra (diamond)? Answer: For instance, a vajra (diamond), compared with all other jewels such as maṇi gems, pearls, lapis lazuli, conch shells, jade, coral, and so forth, is the most solid and durable; it can pierce and destroy all other precious objects, but cannot be pierced or destroyed by other precious objects. Likewise, this samādhi, among the samādhis of all those still in training (śaikṣa), is the most supreme, the most excellent, and the most solid and durable; it can destroy all afflictions and cannot be obscured or subdued by the higher afflictions. Therefore this samādhi is named with the metaphor of a vajra (diamond).

Those from the first fruit to the third fruit are all still in training (śaikṣa), because they still have afflictive outflows that have not been eradicated and still have dharma to cultivate; since their afflictions have not been fully eradicated, or they have not yet eradicated afflictions, they still have to cultivate and train in order to exhaust afflictions. When afflictions are fully exhausted, one is an arhat of the fourth fruit, because there are no more outflows and no more afflictions to be eradicated, no more dharma to cultivate, and one no longer needs to train in the truths of the path of liberation; one has already reached final purity and has already been liberated from all forms of existence in the three realms, and therefore is called one beyond training (aśaikṣa), whereas those before the third fruit are not so. The samādhi attained by the third-fruit practitioner is more excellent than that of the first and second fruits; it is the most solid and durable, and is named the vajra samādhi.