大毘盧遮那經供養次第法疏 2.51

2.51

However, this mantra takes the initial syllable Sa as its substance. Sa (entering) has the meaning of outflow; standing has the meaning of firmness; entering the gate of the syllable A, there is neither outflow nor firmness. If there is firmness, it is a dharma of arising, ceasing, and disintegration. If it is made identical to the syllable A, this firmness is originally non-arisen, which is attaining sovereignty amid all dharmas, equaling space, capable of being an island of all jewels. In my humble opinion, Śākyamuni, through the power of great compassion, when all bodies are dense and tight like vajra, causes even icchantikas to shatter this view and enter the Buddha-Dharma. His vow of bestowing the great jewel—how could this not be attaining sovereignty among all dharmas and being able to shatter all firmness? As such, for those who recite in the method of Vairocana or Śākyamuni, it is as the body is adorned. The root sūtra distinguishes other sūtras. Should also be as the previous upāyas refers to this sūtra. The contemplation of syllable-gates refers to the seed-syllables. If relying on this Tathāgata practice excludes bodhisattvas, vajradharas, and so forth. The great compassion womb refers to the Tathāgata's deeds of great compassion. The king refers to Vairocana. Attaining the ācārya abhiṣeka refers to attaining the abhiṣeka of an ācārya who transmits the Dharma, like receiving the full precepts in the vinaya. The vidyādhara abhiṣeka is like one who has not received the full precepts in the vinaya: one only performs the recitation of one's own iṣṭadevatā's mantra and mudrā, and may not extensively practice and study. If one wishes to study everywhere, one proceeds until receiving the Buddha's empowerment. After having attained empowerment through sincere recitation, one requests an ācārya who transmits the Dharma and receives the universal-study ācārya abhiṣeka, and only then can one extensively practice. The four-limb dhyāna refers to the iṣṭadevatā and so forth; it not only eliminates afflictions, but is complete with the rules for the practitioner. The fundamental method refers to entering the Buddha-samaya and so forth.