The Ngondro practice is very important in order to purify bad karma and to generate wisdom. Actually, our main practice is Mahamudra, but you cannot practice Mahamudra without purification and blessing. In this respect the 'Preliminary Practices' are the most essential.
Until now you have been in samsara, and, as long as this is the case, you experience disturbing emotions. If this was different, you would already be enlightened. In the past, no matter where you were born, you experienced various poisons of the mind. No matter whether you belonged to the higher realm of people or whether you were born in the lower realms. Your present state is proof of that, because if it had been different you would not experience disturbing emotions now.
As long as these disturbing emotions were inside you, you were accumulating bad karma. However, it is not as if there had always been a certain karma accumulated which ripened to a certain result, and which would disappear completely after that, such that now only the karma for our present human life was left over. No, you have millions of different karmas from many past lives, and in only one day you create a lot of new karma through your thoughts, speech and actions. Sometimes it is positive, sometimes negative but unfortunately, it is most often negative because we, as human beings, constantly have disturbing emotions which never result in anything positive.
This does not mean that one should look down on oneself, but that one should accept the present situation - this is the present karma, and it prevents wisdom from appearing. This wisdom is already there, it is the nature of our mind, but it is covered by disturbing emotions. Out of our disturbing emotions we create karma, the result of which is samsara, which again makes us create new karma.
So the karma is very strong, and we have to weaken it by doing the 'Preliminary Practices' until it cannot be harmful to us any more. At the same time, we practice the accumulation of merit by the Mandala-Offering, the third part of the Ngondro practices, in order to create inside us all the conditions necessary to reach enlightenment.
After that, when we are free of karmic influences and have accumulated all the positive conditions, we can successfully begin the Mahamudra practice. If, however, after 111,111 repetitions of each of the four practices, one realizes that no development has occurred, one has to continue to work hard in order to weaken the negative karma.
While practicing Ngondro, many good signs may appear. They are an indication that a result has been reached. But one should not have too many expectations regarding these signs. They should appear naturally and should not be produced artificially.
After practicing a lot of Ngondro, one receives the Mahamudra teachings. It would not be very beneficial to teach the Mahamudra before that because you would not understand the teachings precisely. The mind must be purified in order to do that.
Also, the more profound aspects of Mahamudra are not taught too early on, as one would not be able to appreciate them at a later time. If one has not understood the precise meaning, but has heard a lot about it all the time, it would be boring later. For this reason, great masters like Milarepa and Gampopa had transmitted the Mahamudra teachings only in a very restricted manner. They say that the Preliminary Practices are more profound and more important than the main practice, because Ngondro creates the necessary conditions for the Mahamudra practice. Mahamudra enables you to reach enlightenment within one moment, but in order to do that, you first need these conditions.
With Ngondro you turn yourself into a 'qualified practitioner'. However, this does not mean that after you are finished are fully qualified because, in addition to that, you need a good understanding of the Dharma. For instance one should know the teachings about the qualities of the Buddha nature very well. This subject is explained in the Uttaratantrashastra, in Tibetan Gju Lama. Other important texts one should study are The Distinction Between Consciousness and Wisdom (tib.: Nam-she Yeshe) and 'Showing the Essence of the Buddha Nature' (tib. Nyingpo Tenpa) [both texts were written by the third Karmapa Rangjung Dorje]. The Nyingpo Tenpa is a short version of the Gju Lama.
It is also important to know the Madhyamaka teachings. Madhyamaka explains in what way samsara is an illusion, and that the Buddha mind is beyond this illusion. As a result, one understands that samsara, and also the mind itself, are only delusions and that the Buddha mind is something completely different altogether, something beyond this illusion. However, it is not different in the sense that it is separate from the present mind. Both are inseparably one. Madhyamaka explains exactly in what way the nature of your present mind is the Dharmakaya. But the Madhyamaka is not able to point out the Dharmakaya as something special like one could point at a flower and say, 'This is a white rose.' What the Madhyamaka can do is exactly show the nature of the illusions. Apart from that, there is something that you have to recognize and understand by yourself - the Mahamudra realization. For a meditator on this path, it is very important to learn about the philosophical views of the Madhyamaka.
The Madhyamaka also explains that cause and effect will apply as long as the mind is under the influence of illusions. Positive or negative causes always lead to the corresponding results. This is why meditators with the Madhymaka view have great respect for the law of karma. Even Bodhisattvas on high levels will experience the results of unpurified actions in the postmeditative phase. Due to their great merit, the results will generally be good; but in the postmeditative phase disturbing things may also appear.
So the Madhymaka is very important, as it gives you a fundamental understanding of the whole Dharma.
Today, good scholars have also published books with short, comprehensible explanations about certain parts of the Abhidharma. Here, for instance, the different stages of the Shine meditation which the meditator goes through are explained.
During the continuous development of the Shine meditation, there are many details where the philosophical view on the different levels affects certain forms of ignorance and disturbing emotions in the mind. It is important to know these details precisely because, when you rest in deep meditation, you are more likely to be led by your deep knowledge rather than by an outside person. If you then have good knowledge, you will not encounter any obstacles. Without this knowledge, however, there are many risks of being misled during meditation. Sometimes one may perhaps follow wrong views which one considers to be right. Some other time one does not know how to deal with certain intellectual problems because one does not know the necessary methods for this task. One may also get agitated about certain experiences although one should not be attached to them.
At that point one needs a good meditation teacher, otherwise there are many dangers. For instance, if you do a practice for the accumulation of merit, you need a teacher who knows about that. The teacher should know about this practice although he does not necessarily have to have mastered all the other Dharma subjects.
When one is confronted with experiences during meditation, then one needs a teacher who is very qualified in this respect. In this context I always enjoy telling the story about Gampopa who once had a problem with his meditation practice - all of a sudden he could not see anymore. Gampopa crawled to Milarepa and asked him what he should do, and Milarepa answered, 'Your meditation belt is too tight. You should loosen it.'
If the meditation teacher has no experience of his own, he cannot teach you anything. In which book can you find the information about the situation in which the meditation belt is to be loosened? Such books do not exist. Geshes and Khenpos could study all Buddhist subjects for 25 years, but within all the books there will not be one which explains such things because the number of beings is infinite. Who could describe all the individual problems of all beings of the past, the present and the future? So when you come to these meditation experiences, the teacher needs to be qualified.
Another important point is the development of the Bodhisattva mind. It is the cause for our development from one lifetime to the next. For this reason, all Mahayana and Vajrayana teachers advise concentration on Bodhichitta, the state of mind of the Bodhisattva.
The 'Bodhisattva vow' helps to develop our good parts and to become helpful for other beings. It prevents us from falling into lower realms as a result of anger or jealousy, etc. Even if such disturbing emotions arise, the Bodhisattva vow immediately purifies them, which is why one should never give up developing Bodhichitta.
Anger and jealousy directly affect your Bodhichitta, and the ego is another bad enemy. These three mind-poisons are the reason why beings are always so aggressive. There is so much anger everywhere, and when energy is connected with that anger, beings become dangerous to others and create in themselves the causes for the lower realms. The Bodhisattva vow is one protection against the lower realms. The accumulation of merit, by doing the Mandala practice for instance, is increased by the Bodhisattva vow as well as the power of the purification practices.