"The blue heaven beyond the clouds"
The phrase at the lower side of this picture is
"The frog in the well knows nothing of the great ocean. But he knows the blueness of the sky very well."
The first phrase generally means
"He has narrow thoughts and knowledge and doesn't know there is a wider world. "
But in the whole sentence it means
"He doesn't know the size of the ocean.But he understands very well the blueness of heaven is wider and deeper. "