If one owns a non-Jewish slave, and he knocks out the slave's eye or tooth, the slave goes free, as it states (21:26-27) עין את איש יכה וכי שן ואם עינו תחת ישלחנו לחפשי ושחתה אמתו עין את או עבדו שנו תחת ישלחנו לחפשי יפיל אמתו שן או עבדו.
What is the reason for this halachah? The Rabbeinu b'Chayei explains: Cham saw his father, Noach, not dressed, and Cham told his brothers about this (see Bereishis 9:22). So, Cham sinned with his eyes and with his mouth because [a] he saw his father undressed and [b] he told his brothers about it. His punishment was that the descendants of his son, Canaan, would be slaves. When a slave's master knocks out a tooth or an eye of his slave, he goes free. This is because the tooth and the eye are the root of his slavery. If they are knocked out, the slave can go free.
From here, we see the importance of guarding the mouth and the eyes.
Someone told the Ruzhiner that his eyes hurt him. The Ruzhiner replied, "How do you know that your eyes hurt you? Perhaps you hurt your eyes."
An Arab was hired to deliver bags filled with merchandise. For each bag delivered, a shekel was placed in a dish. This was done to keep track of how many bags were delivered. When the delivery was completed, they would count the coins to know how many bags were delivered and what the charge would be. Once, when the Arab noticed no one was watching, he took a handful of the coins from the dish and placed them into his pocket. He thought that he was gaining but was losing way more.
The nimshal is that when people sin with their mouths or eyes, they think they are gaining something – a juicy lashon hara, and the freedom to look wherever they want – but they are losing so much more.
The Rokeiach writes that when Hashem wants to give wealth or honor to a person, the Satan says, "Let's test him first to see whether he deserves it." The Satan tests him with his eyes. The Satan is a malach hamashchis, a destroying angel because he harms people and takes away the blessings that would have come to them. They end up losing because of the eyes.
