This is a calligraphy by Jiko Tsusho, the 55th Abbot of the Obaku Zen sect. The inscription is "Sanshiki Shojo Shin" (山色清浄身), taken from a Zen phrase. It means that the very form of the mountain is none other than the pure mind (Buddha-mind) of a Buddha, and is a quote from a verse of a Chinese poem from the Song Dynasty. The condition is relatively good, but please note that there are some stains due to the work being over 50 years old.