大毘盧遮那經供養次第法疏 2.65

2.65

囉是塵義，入阿字門即是無塵也。所以三重者，謂除凡夫二乘塵障。𤙖是恐怖義，以大威猛自在之力怖彼三重塵障，令得除淨而同佛眼也。闍，此最後字，是種子也，諸字皆為釋此字義，即生不生是闍字義也。或以初薩字為體，亦同得用之，是驚覺義也。吽字中有訶字，是歡喜義。上有大空點，是三昧。下有字亦三昧。上者三世諸佛皆同此觀三昧中行也，故名等觀也。

RA means dust; entering the gateway of the letter A, it is without dust. As for why there are three layers, it means dispelling the dust-like obstacles of common people and the two vehicles. HŪṂ means terrifying; by means of great, fierce, sovereign power it terrifies those three layers of dust obstacles, causing them to be purified and become identical with the Buddha-eye. JA: this final syllable is the seed; all the syllables serve to explain the meaning of this syllable, that is, arising and non-arising is the meaning of the syllable JA. Or, taking the initial syllable SA as the substance, it is also equally functional; it means awakening. Within the syllable HŪṂ there is the syllable HA, which means joy. Above there is the great anusvāra dot, which is samādhi. Below there is a syllable that is also samādhi. The upper means all Buddhas of the three times equally practice within this samādhi of contemplation, hence it is called 'equal contemplation'.