it’s come from 观书有感二首 It’s writer is “zhuxi”(朱熹) He came from Song dynasty . the title is means he has some thought when reading books
The square pond with half an acre size looks like a mirror, it's clean and bright.
The shine of the sky and the shadow of the clouds are reflected in the pond, they are swinging and full of energy.
If you wonder why the spring is so clear,
it is because the source is continuously supplying living water.