Zazen (seated mediation)
In the Rinsai tradition, seated mediation is just one means of gaining insight, concentration and mental self control – skills which over 700 yrs ago the Kamakura samurai noted to be very helpful to their warrior skills. Initially one trains concentration (watching breath for example) to develop skills that allow progress to the next level. Satori (enlightenment) is the ultimate goal.
The calligraphy in the picture is that for Mushin.