If a Saraat affliction will be in a person... (Vayikra 13:9)
Lashon hara (negative speech) is a very serious sin and results in the transgressor being afflicted with Saraat a leprosy-like illness. Why is the sin of lashon hara so severe that it must be punished with Saraat?
The Torah states, "And [G-d] blew into his nostrils the soul of life; and man became a living being." (Bereisheet 2:7) Onkelos translates "a living being" as a "speaking spirit." Accordingly, it is the soul that gives a person the power to speak. Because the soul and the ability to speak are directly connected, great damage is done to the soul when someone sins through speech. Lashon hara is therefore punished severely and instantaneously.
Rabban Shimon ben Gamliel once sent his servant, Tavi, to buy "good food." Tavi, who was famous for his wisdom, brought back a tongue. Thereupon, Rabbi Shimon sent him to buy some "bad food." Again he returned with a tongue. Rabbi Shimon asked him to explain how the same food could be both good and bad. Tavi answered, "From a tongue can come good and bad. When a tongue speaks good, by complimenting or praising another, there is nothing better. But when a tongue speaks evil, when it tells lashon hara or makes fun of people, there is nothing worse. It can break up families and kill.
The verse states, "Death and life are in the hands of the tongue." (Mishlei 18:21) The tongue is mightier than the sword. A sword can only kill someone nearby, whereas words spoken on one continent can "hit the heart" of someone on another continent. The tongue, of all the limbs and organs, moves with the least difficulty and most speed. Consequently, lashon hara is one of the sins committed most frequently. It is for this reason that the mouth is guarded with two gates: the teeth and the lips. A person has to think twice before he says something once.