This meaningful phrase is spoken by the fox to the little prince in the above mentioned, very popular french book for children, which means ~
One can only see well with the heart. The essential is invisible to the eyes.........
How beautiful and how true....! the air we breath, the fragrance of a flower, feelings of the heart, relations, passions, emotions, warmth of a touch.....are'nt these all invisible? Can we imagine living without these.....?