There should be neither Yin nor Yang in the highest level, but most of the time we are either too Yin or too Yang. In Taoism, there is a Tai Chi Circle, half of it is black with a white spot in the center; the other half is white with a black spot in the center. That shows the situation of Yin and Yang. Most of us have too much Yin and very little Yang, and sometimes we are completely Yin without any Yang, but some people have too much Yang and hardly any Yin.
We shouldn't like either Yin or Yang too much, but now we are still unable to do it. After practicing Quan Yin Method, we are able y to control Yin and Yang, and then we can use it instead of being used by it. Now we are all used by Yin and Yang. When Yin comes, we are fierce and angry s and couldn't bear anymore; when Yang comes, we are so happy and joyous. It comes all by itself, not on our wish; we cannot put Yin and Yang in a bag, and take out Yin or Yang whenever we need them and as much as we need just like we do with money.
Our mind is very powerful; whatever we wish for will come true. So we say, "Everything is created by the mind." After we practice spiritually, our mind power becomes even greater, because we are using the power of our own. Enlightenment means opening this power so that we can use it every day after that. At that time, our body, speech and mind should all be clean, otherwise if we use such a great power to think about bad things, won't that be worse?
Therefore, clean body, speech and mind are the most important for spiritual practitioners. Master told you to be vegetarian, in order to nurture your compassion, so that you can use it in good aspects when you are grown up.
Shakyamuni Buddha said, "If those who practice spiritually and meditate don't eat vegetarian, they can't become Buddha; they will become the King of Maya at the most." It's already not bad to become the King of Maya, because the King of Maya is a very high position within the three worlds. He controls what happens in the three worlds, and is the king within the three worlds. Brahma is the highest position for the King of Maya, with a great power and incredible magic power, but he can't go beyond the three worlds, because he is lacking in compassion and haven't mastered the balance of Yin and Yang, with a lot of Yin and very little Yang. That's the difference, so don't ask Master why we should eat vegetarian. You must eat vegetarian if you want to go beyond the three worlds, because compassion is very important. If we have the power but no compassion, we may misuse that power.