an excerpt from" The Manure of Experience and the Field of Bodhi" chapter
"It is said, I think in the Lankavatara Sutra, that unskilled farmers throw away their rubbish and buy manure from other farmers, but those who are skilled go on collecting their own rubbish, in spite of the bad smell and the unclean work, and when it is ready to use they spread it on their land, and out of this they grow their crops. That is the skilled way. In exactly the same way, the Buddha says, those who are unskilled will divide clean from unclean and will try to throw away samsara and search for nirvana, but those who are skilled bodhisattvas will not throw away desire and the passions and so on, but will first gather them together. That is to say, one should first recognize and acknowledge them, and study them and bring them to realization. So the skilled bodhisattvas will acknowledge and accept all these negative things. And this time he really knows he has all these terrible things in him, and although it is very difficult and unhygenic, as it were, to work on, that is the only way to start. And then he will scatter them on the field of bodhi. Having studied all of these concepts and negative things, when the time is right he does not keep these anymore, but scatters them and uses them as manure. So out of these unclean things comes the birth of the seed that is realization. That is how one has to give birth. "
Chogyam Trungpa Rinpoche in Meditation In Action