A stringless lute, a valley without an echo

[RichardH]

Some years ago I heard the terms "a stringless lute" and "a valley without an echo". They were referenced by Korean Master Chinul in his "straight talk on the true mind". A compilation of his teachings translated by Robert Buswell (Tracing Back the Radiance) was the handbook of the Korean Sangha I was practicing in at the time. I thought they were beautiful and suggestive but could not connect with them. These phrases have been popping up lately, inspired by rolling around the idea of "The person of no rank", and Zazen.

What does a stringless lute and a valley without an echo mean or evoke for you?

Thanks

Gassho Daizan