A Zen Poem

I have just been sent this poem by a friend from the Newport Soto Zen group. It is by Yunng-Ming Yen-Shou

Immovable Mind

You wish to know the spirit of Yung-ming Zen?
Look at the lake in front of the gate.

When the sun shines, it radiates light and brightness,
When the wind comes, there arise ripples and waves.

What does the poem mean?

Yung-ming Yen-shou (904-975) was a Buddhist monk who lived in a period of broad changes in Chinese society and Buddhism. He played a leading role in the restoration of Buddhism in the Wu Yueh kingdom, and left a large body of writings. One of the best known works, the Wan-shan t'ung-kuei chi ("Treatise on the Common End of Myriad Good Deeds"), has long been cherished by the tradition for its advocacy of harmony between Ch'an meditation and Pure Land practice.