The essential twelve-syllable mantra, also known as the Vajra Guru Mantra, is explained according to the extensive commentary on The New Treasure Preliminary Practices called The Lamp Illuminating the Path to Liberation as follows.
OM, AH, and HUNG are the expression of the three vajras of enlightened body, speech, and mind that begin the mantra.
BENZAR is vajra. Vajra means never affected by the elaboration of dualistic conceptions. Abiding as the essence of all-pervasive empty awareness, vajra is Dharmakaya.
GURU means the Sambhogakaya Lama. The nature of this Sambhogakaya deity has the seven branches of union, carrying the inexhaustible opulence of the qualities of enlightened body and vast oceans of purelands arranged like gatherings of clouds. This is Sambhogakaya.
PADMA is the radiant awareness of discerning wisdom, the vajra speech of great bliss. Arising in the form of the supreme Lotus family of miraculous birth, this is Nirmanakaya. By remembering the greatness of the qualities of this Great Lama Orgyen Dorje Chang, who is the inseparable Three Kayas, pray from the state of the uncontrived nature of one’s mind, free from elaboration. By the power of prayer, both common and supreme SIDDHI without exception are requested with HUNG, and received within one’s mind right at that moment. Thus, remembering the meaning, recite the mantra.