I noticed that a few people here are asking about bowing. I think we usually interpret it as a greeting or sign of respect or paying homage to someone or something. In our Zen practice, we interpret it as part of our spiritual training. It is not simply to go through the motions, but it is important to bow with the proper frame of mind.
We often teach new students that bowing is a way to purify the mind by releasing our egos.
Some interpret bowing as a way to recognize the Buddha-Nature in the other person. In this regards, in Zen thought, all living, sentient beings already have the Buddha-nature or seed of enlightenment from the beginning. When we bow to a person, we recognize his enlightenment and Buddha-hood. The purpose of training is to come to this realization within one's self or to refine this knowledge.
Of course, in Japanese culture, one sees bowing everywhere. Today, it is much less, I think, but several decades ago, we even see Japanese bowing to the telephone or to the other person while speaking on the telephone. I always thought it was the natural thing to do until a friend of mine started to laugh at me. I didn't know what was wrong until he pointed out that while I was on the phone, I was actually bowing several times to the other's conversation. After that, I became very self-conscious, because I thought it was pretty funny too! Why should I bow when the other person can't even see me? Bowing is not just a sign of respect but it is a way to say, "thank you" and bowing on the phone only means that I am thanking the other person. To show my appreciation and gratitude, he can be there or not.
Bowing means to recognize the "worth" of the other person. In the tea ceremony, one bows to the cup of tea, in appreciation of the tea and to say "thank you" to the tea itself. The tea gives up its "life" so I can enjoy a drink, so I should say "thank you" to the tea. In Japanese culture, it makes sense to me. If I look at it through my Western mind, I think, "how odd!" why we can bow to an inanimate object in Japanese culture is the old idea of "ikasu" or "give life to everything." It is an old idea of giving our energy or spirit to everything we come in contact with.
In Japanese feudal culture, bowing is looked upon as a symbol of the vertical hierarchy. If we look at bowing from the standpoint of Japanese culture and the "spiritual" life contained within, the act of bowing is much more refined and profound.
For O'Sensei, I imagine that more than just a sign of respect and social custom, I think bowing was part of his spiritual practice. . . . .
Just as people determine a person by the way he shakes hands with you. In Japan, we can tell the person's character by the way he bows. When we bow to each other, before and after practice and to O'Sensei, it should always be done with great dignity and beauty. Finally, we must always bow with a very strong "ki" or energy because when we bow to the other person, we give him a bit of our spirit.