Ven. Thrangu Rinpoche
One may have doubts about how Buddha nature is changeless and always present, but will not manifest because of impurities. To illustrate this there will be nine examples of Buddha essence and the impurities.
When the Buddha gave teachings, he didn't simply declare the truth, but he gave reasons for what he was saying. The reasons for his teachings were sometimes very apparent and at other times very obscure. The obvious reasons for his teachings are the ones grasped by using our senses. There are, however, teachings which cannot be grasped with our sensory faculties - these are objects which are either very far away in space, or very remote in time, or due to karma. If one has a particular karma, one's sphere of experience will prevent one from experiencing other types of lives and so one is limited. Since one cannot understand the more hidden meanings directly, one has to understand them through inference. For instance, if one says there's a fire behind that hill because there is smoke, no one can see the fire because it out of view, but one is believed because smoke is a valid sign of a fire. For a sign to be valuable it must have universal applicability i.e., whenever there is a fire, there must be smoke. The sign must also be valid, if one says there's a fire because I see a tree, it is an invalid sign. So a sign for showing the presence of something that is hidden must have universal applicability and be a valid sign. The presence of Buddha essence is proved by means of valid reasons of the three fold marks of valid proofs given above. This is used in the context of examples and with the examples one proves its validity. When proven by an example, it then applied to Buddha nature itself.
First, the nine examples of beautiful things covered up by impurities are listed and then the nine impurities are listed followed by a list of the pure things. These will be elaborated below. The method for presenting the examples is the same: first a verse giving the example, then a verse giving its meaning, and finally a verse presenting the parallel between the example and Buddha nature is given.
1. Imagine an ugly, withered lotus covering a beautiful Buddha statue. Someone with clairvoyance would see the statue and think that this was not a good place for such a beautiful statue and would break open the lotus shell and remove the statue. Similarly, Buddha nature is in the mind of all beings even those in the worst hell but it is obscured by the defilements of the three poisons. The Buddhas with divine vision and great compassion see this Buddha essence and help beings out of the shell of defilements. Individuals with Buddha nature need to reach Buddhahood so they do not continue to suffer in samsara therefore they need the Buddhas with their vision and their teachings to receive the tools to make this Buddha nature manifest.
2. Imagine some tasty honey which is surrounded by swarming bees. If an experienced person knows how to separate the honey from the bees, then persons can enjoy the honey. The meaning is the Buddhas with the omniscient eyes of twofold knowledge can see the Buddha nature in all beings which is like the honey. The bees circling the honey could be removed because they weren't part of the honey and in the same way the impurities of beings aren't part of the Buddha nature and therefore can be removed and the Buddha nature can manifest. In this example the man who knows about honey is like the Buddhas who are skilled in removing obscurations which are the bees.
3. Imagine a grain of rice enclosed in its husk. In the husk it is inedible so it cannot manifest as food. Kernels of rice, buckwheat, and barley cannot be used as good food when they are unhusked and similarly as long as Buddha nature called "the lord of all qualities" in the text is not liberated from the shell of impurities it cannot give the taste of the joy of dharma to beings.
4. Imagine an individual going on a journey and on his way he looses some pure gold which falls into some rubbish. It remains unchanged for hundreds of years being quite useless. Then a god with clairvoyance sees the large lump of gold in the rubbish and tells someone where to find this valuable thing so it can be put to its proper use. The meaning is the Buddhas can see the pure Buddha nature of beings which has fallen into the filth of defilements and has been lying there for hundreds or thousands of years. Even though it has been there, it has not been polluted by the defilements. If there were no rubbish there is the first place, there would be no need to have the clairvoyant person come along. Also if there had been no gold for the clairvoyant person to point out, it would have been pointless as well. Similarly if Buddha nature were not obscured by defilements, there would be no need for Buddhas to come into this world and teach about Buddha nature. Also if beings didn't have Buddha nature from the beginning, there would be no need for Buddhas to give teachings because it would be impossible for individuals to attain Buddhahood. This is why the Buddhas come and give teachings and point out our obscurations. They do this by producing the rain of dharma which has the ability to wash away little by little the impurities which we have accumulated. Gold is very useful, but if it is covered by rubbish it is useless. This is why this clairvoyant person tells someone where it is and tells him to remove the rubbish and use the gold. In the same way the Buddhas tell us about the rubbish of all our instability. They see beings who have the wish-fulfilling gem in their hands, but it is being wasted. Beings are suffering, but they have the tool to eliminate the suffering without knowing it. This is why the Buddhas teach the dharma. We remain stuck in problems and difficulties and don't have the power to realize our own goal. We might think there is nothing we can do about it, but since we have the knowledge of how-it-is and manyness, we have what is necessary to remove the defilements. The Buddha came to tell us if we practice, using what we have, we can reach enlightenment.
5. Imagine a man so poor that he doesn't have any food or clothes living in a house built over a great treasure. If the man doesn't know about the treasure, he will continue to suffer in poverty because the treasure cannot say, "Look I am here." The meaning of this example is that all beings have the great treasure of Buddha nature in their minds and this treasure doesn't need to acquire new qualities because it has always been there. We do not see the Buddha essence in our mind so we endure all the sufferings of samsara caused by the defilements. The parallel is the treasure doesn't tell the man "I am here" even though it is very close by. Similarly all beings have the precious treasure of the dharmakaya locked in their mind, but continue to have the sufferings of deprivation. Therefore the great sages, the Buddhas, come into our world to help us find this nature.
6. A very tiny seed in a fruit has the power to be an enormous tree. One cannot see the tree in the seed, but if one adds to the seed all the right conditions for growth such as water, sunlight, soil, etc., a great mighty tree will develop. The meaning is that Buddha essence exists in all beings but it is encased in the peel of ignorance which generates our emotional and cognitive obscurations. If one practises virtue, it will generate the favorable conditions for this seed of Buddha nature to grow. Through the accumulation of knowledge and virtue the seed will develop into the "king of victors" or Buddhahood. The parallel is that just as a tree grows from the skin of a fruit and with the proper conditions will grow into a tree, Buddha essence is enclosed in the skin of defilements and with proper conditions will manifest into Buddhahood.
7. Imagine a very valuable Buddha statue wrapped in tattered rags and abandoned by the side of the road. A passerby would notice it, but if a god came along, he could tell how to find the statue. The meaning is the Buddhas can see with their jnana that Buddha nature in beings wrapped in the tattered rags of the defilements. They see this in persons and even in animals. In the same way a god can see a statue with divine vision, so the Buddhas can see Buddha nature lying on the road of samsara inside the rags of defilements. They tell beings to remove the tattered rags so the Buddha nature can manifest in its complete purity through the dharmakaya.
8. Imagine a destitute ugly woman who had no place to stay and therefore ended up in a pauper hostel. Also imagine that she is pregnant and holds in her womb the future king. She continues to suffer because she doesn't know anything about it. This is similar to the way beings hold the precious Buddha essence but do not know anything about it or get any help from it. In the same way as the woman in the hostel, this king is in the womb, we are born in the Six Realms of Samsara; are born as humans, some as animals, some as Preta Spirits. All have to suffer - animals suffer from enslavement, spirits have to suffer from thirst and hunger, humans have to suffer from birth, sickness, old age, and death. All of us are like the poor woman living in pain. Even if we are totally destitute and have no happiness, within us is the seed which can terminate all our suffering - we have Buddha nature. The poor woman who has a great ruler in her womb is ugly and dressed in dirty clothes. Because she doesn't know that she bears a king she remains in poverty and is very unhappy. In the same way beings have a protector inside their mind, but are unaware of this so they have no peace of mind and are overpowered by defilements so that they remain in samsara and undergo all kinds of suffering.