The essence of the Buddha’s three turnings of the wheel of Dharma brought into practice - this is the ngondro

Generally speaking, there are two principal qualities of the mind. The first one is emptiness. And the second is clarity. And in order for Buddha to teach people to realize these qualities of the mind He taught the teachings on The Four Noble Truths – the First Turning of the Dharma Wheel. The First Dharma Wheel is basically for the foundation, for the realization of the meanings that were taught in the Second Wheel Dharma and the last, the Third Wheel Dharma. The essence of those three subjects that are taught by the Buddha Shakyamuni, or the teachings of the Buddha are brought into practice, into one package – this is the ngondro practice. It basically covers everything. Therefore, this is very simple and very important. But I know people don’t understand the value of this and people always look for something great that is beyond their mental capacity and they will be loser in the end.

  Hungkar Dorje Rinpoche, GURU YOGA: The Source Of Power In Speech and The Purification”