The actual purification of your nature: the ordinary aspects are the four changes of mind; the extraordinary ones are the refuge, generation of Bodhicitta, purification of obscurations, and the two accumulations. Having practiced each of these assiduously according to the commentaries until you have truly experienced them, you should then consider the most extraordinary Guru Yoga, as the vital essence of practice, and persevere in it.* If you do not, growth of meditation will be tardy; and even if it grows a little it will be very vulnerable to obstacles and genuine understanding will not be able to take birth in your being.

So, if you pray with simple and very fervent devotion, after some time, through the transfer of the Heart-Mind realization of the Guru, and extraordinary understanding, inexpressible in words, will certainly take birth within. As Lama Shang Rinpoche said:

“To nurture stillness, experiences, deep concentration – these are common things.
But very rare is the realization born from within through the Guru’s blessings, which arise by the power of enthusiastic faith.”

Therefore, the birth of understanding in your nature of the meaning of the Great Perfection depends upon these preliminaries. That was what Je-Drigung meant when he said:

“Other teachings consider the main practice profound, but here it is the preliminary practices that we consider profound.”

* The four changes of mind arise from the contemplation of the preciousness and rarity of the human body, of the impermanence of all things, of the ineluctable law of cause and effect and of the imperfections and sufferings of Samsara. The Guru Yoga of Lamai Nal-jor, literally union with the Guru’s nature, is not only the essence of the preliminaries but also of all practices.

Extracting the Quintessence of Accomplishment  ~ pages 5-6
by Jigdral Yeshe Dorje
Translated according to the golden explanations of  Tulku Thondup Rinpoche,
Dungsey Trinley Norbu Rinpoche, and Taklung Tsetrul Rinpoche,
and with the kind assistance of many vajra brothers and sisters.
Originally published in 1979 by Orgyan Kunsang Chökhorling
Reprinted in 1998 by Vajrayana Foundation