Essential Tibetan Buddhism, p. 110

After Atisha passed into final liberation, Drom the Teacher became his successor. On one occasion his three main disciples, the brothers Potowa, Chengawa, and Puchungwa, asked him, "Please tell us the way of practice that includes the essence of all paths to omniscient Buddhahood."

The spiritual friend Drom answered, "though there is an incalculable number of precepts, each of which gives entry to the path of enlightenment, if one has the necessary ground for practice, there is only one thing to attain."

"What is that one thing?" asked the three brothers.

"That which has the essence of voidness and compassion. To explain: things are naturally and truly unborn. Compassion is the relative spirit of enlightenment; it is universal compassion reaching out to all beings who have not yet realized their fundamental birthlessness. Thus those who practice the path of the Universal Vehicle should first strive to develop these two forms of the spirit of enlightenment. Once the spirit of enlightenment has been conceived, it should be diligently cultivated. By doing so, one is sure to realize Buddhahood with its Form Body and Truth Body, the ultimate fruition of attaining the two kinds of spirit of enlightenment.

"There are many methods to conceive of the two kinds of spirit of enlightenment. Condensing then into a way of practice, there are only three root methods and nine branch methods growing from them. The three root methods are mind development, the accumulation of merit and wisdom, and the quest for samadhi. Each root method has three principal branches.

"The three principal branch methods of mind development are the meditations on impermanence, love and compassion, and the selflessness of all persons and things. Among the various methods of mind development, these three are the most important, incorporating all the others.

"The principal branch methods for the accumulation of merit and wisdom are to honor the Mentor, to venerate the Three Jewels, and to honor the Sangha. These three are the only important methods, incorporating all others.

"The principal branch methods of the quest of samadhi are to maintain impeccable ethical conduct, to pray to the mentors of the lineage, and to keep constant solitude. In seeking the supreme samadhi of quiescence and insight, these are the only important methods, incorporating all the others.

"By practicing these nine methods, you will naturally develop the two kinds of spiritual enlightenment. When you develop the absolute spirit, you will effortlessly realize that all outer and inner things are empty of reality status, originally lacking true creation, and utterly free from proliferation. This realization will bring you boundless joy. When you develop the relative spirit of enlightenment, you will feel a profound love and compassion for those beings who have not realized the absolute spirit of enlightenment. From then on, whatever you do will only be for the benefit of those many beings, and, since you have attained the spirit of enlightenment, all you have already done will benefit them also.

"There are two ways integrate absolute and relative spirits of enlightenment. When you develop the absolute spirit, you experience the voidness of all existence; at that very moment of experience of voidness, you will develop intense compassion for all beings, since they are not negated by the experience of voidness. When you develop this relative spirit of enlightenment, this profound compassion for all beings, you will simultaneously feel the nonseperation of self and others. Appearances are like a magician’s illusions; they are actually devoid of intrinsic reality.

"When you have successfully developed this integrated realization of the two kinds of spirit of enlightenment, you have correctly entered the path of the Universal Vehicle. By cultivating that realization, you will perfect your meditation and will naturally obtain the Form and Truth Bodies of Buddhahood. The Truth Body arises from voidness, the absolute spirit of enlightenment. The Form Body arises from compassion, the relative spirit of enlightenment. From the cultivation of the indivisible two kinds of spirit of enlightenment, you will reach the indivisible Truth and Form Bodies of Buddhahood."