Dear Roshi What is 'to polish one's mind' and how do we knowfeel that the polishing is taking place?Thanks for taking the time to reply

This is a good question. In  Zen we practice samadhi. You may think that samadhi is some kind of intoxication. That is a mistake. Samadhi is, as the Buddha taught: If you concentrate your mind, there is nothing that you cannot attain. Samadhi is concentration on one thing and letting our mind become distracted. If a piano player is well experienced, he will forget his body and not be aware of the piano. Becoming one with the breath, whether people praise or criticize us, we do not pay attention to it. The same is true for sports, you become the daily training and thus are at one with the motion of the play. And then without thinking about an amazing play manifests. This is called Samadhi in action. During that play, you will be purifying your mind, yet this stops when your play stops. Yet if you make some efforts during your daily life, you can continue this mind of samadhi during all activities of the day. The samadhi of cooking. The samadhi of cleaning. The samadhi of walking. And when that becomes more settled, then you can stay in continued pure mind instance. This is difficult, yet this is the only place of human´s peace. Please carefully keep developing it.