The following excerpt is a Hermetic teaching on self-observation and self-knowledge, speaking to practising having control over oneself both physically and psychologically.
It was taken from Manly P. Hall’s translation of a fragment attributed to the teachings of Hermes Trismegistus called Poimandres, The Vision of Hermes:
“I will not permit the evil senses to control the bodies of those who love me, nor will I allow evil emotions and evil thoughts to enter them. I become as a porter or doorkeeper, and shut out evil, protecting the wise from their own lower nature. But to the wicked, the envious and the covetous, I come not, for such cannot understand the mysteries of Mind; therefore, I am unwelcome. I leave them to the avenging demon that they are making in their own souls, for evil each day increases itself and torments man more sharply, and each evil deed adds to the evil deeds that are gone before until finally evil destroys itself. The punishment of desire is the agony of unfulfillment.”
~ The Secret Teachings of All Ages, Manly P. Hall, Poimandres, The Vision of Hermes (source).