"All things excellent are as difficult as they are rare."

"He who wishes to revenge injuries by retaliating them, will live in a circle of hatred."

"It is impossible for a man to be affected by any emotion unless he imagines something which excludes the existence of an external cause of that emotion."

"The highest activity a human being can attain is learning for understanding, because to understand is to be free."

"The highest virtue of the mind is to know God."