大毘盧遮那成佛經疏 9.70

9.70

右句義中，伽伽那阿難多是虛空無量，薩發囉儜是普遍，毘輸馱是清淨，達摩儞闍多是法界生義。此言如來頂相，猶如虛空，出過數量、普遍清淨。當知如是頂相，從法界胎藏生，非從世間父母胎藏生也。此真言亦以伽字為體。言如來髻相，無去來相同於大空，而一切眾生以去來相觀之，是故周於十方不能見其邊際。若行者以必定心，自知我之頂相亦復如是，是名佛頂真言也。阿闍梨自作毘盧遮那時，解髻而更結之。若出家人，應以右手為拳置於頂上，然後說此真言以加持之，則一切諸天神等不能見其頂相也。

In the meaning of the phrases above: gaganānanta means space-immeasurable; spharaṇa means pervasive; viśuddha means pure; dharmanirjāta means born from the dharmadhātu. This means that the Tathāgata's uṣṇīṣa is like space, transcending measure, pervasive, and pure. One should know that such an uṣṇīṣa is born from the matrix of the dharmadhātu, not born from the worldly womb of parents. This mantra also takes the syllable ga as its essence. It says that the mark of the Tathāgata's topknot has no mark of going or coming, being identical with the great emptiness, whereas all sentient beings view it with marks of going and coming; therefore, searching throughout the ten directions, they cannot see its summit. If the practitioner, with a resolute mind, knows personally that 'my uṣṇīṣa is also like this,' this is called the Buddha-uṣṇīṣa mantra. When the ācārya transforms himself into Vairocana, he loosens his topknot and reties it. If he is a monastic, he should make a fist with his right hand, place it atop his head, and then recite this mantra to empower it; then none of the gods or spirits will be able to see his uṣṇīṣa.