Tea was discovered by Zen masters and tea is not an ordinary thing for them.
In every Zen monastery they have a tearoom. It is special, just like a temple. You will not be able to follow this... because tea is a very religious thing for a Zen master or a Zen monastery. Tea is just like prayer. It was discovered by them.
Zen has a different attitude towards tea.
The very name comes from a Chinese monastery, Ta. There, for the first time, they discovered tea, and they found that tea helps meditation because tea makes you more alert, it gives you a certain awareness. That's why if you take tea you will find it difficult to go to sleep immediately. They found tea helps awareness, alertness, so in a Zen monastery tea is part of meditation. What more can Joshu offer than awareness? When he says: "Have a cup of tea," he is saying: "Have a cup of awareness." Tea is very symbolic for them. He says: "Have a cup of awareness."