Meriting the Hidden Light:

The following well-known words of the Vilna Gaon zt"l (from Igeres HaGr"a, a letter that he wrote to his family) are a tremendous source of inspiration for us all on the topic of shemiras halashon: "Every individual will be judged for every word he says. One should not waste even a small word. Therefore, I exhort you to become accustomed to sitting alone because, as Chazal say, the sins involving the tongue are the worst sins of all. There is no reason to expand on this sin, as it is worse than all other sins... Chazal say that all of a person's mitzvos and Torah are not sufficient to overpower what comes out of his mouth. The work one has to do in this world is to make himself like a mute and to stick his lips together... And all the worst punishments (of Kaf Hakeleh) are because of pointless words that the mouth emits... That is in regards to pointless words, but in regards to lashon hara, rechilus, mockery, words that cause discord and curses, and especially if those are said in the bais knesses or on Shabbos and yomtv, one gets an even worse punishment (and one is sent to an even lower place in gehenim). One cannot even imagine the damage he can cause himself with one word. One should not waste even a single word... And one should not say any unnecessary word on Shabbos or yomtov because the holiness of Shabbos is very great and, as Chazal say, it was only permitted with difficulty to greet a friend on Shabbos. We see how severe one word can be. You should know that for words and middos, one must habituate himself very much to act properly... Until one's final day, he must "afflict himself." This does not mean that he should fast or cause pain to his body. Rather, he must afflict himself by subduing his mouth and his desires. This is how one earns Olam Haba, as is stated (Mishlei 6:23): “The way of life (in Olam Haba) is rebuke and mussar." Guarding one's mouth in this way is more effective than all fasts and physical afflictions. The Gr'a continues: Every single second that a person closes his mouth, he is rewarded with a great, hidden light that no angel or creation can imagine. The pasuk says (Tehillim 34:17-18): “Who is the man who desires life... protect your tongue from evil and your lips from speaking badly..." In this way, one atones for all sins and is saved from Sh'ol Tachtis, as is stated (Mishlei 21:23): “One who watches his mouth (from excessive eating) and his tongue (from speaking bad words), protects his soul from suffering." The main thing is not to speak even positively about any man, and certainly not negatively. The main way to merit Olam Haba is by guarding one's mouth. This is bigger than all of one's Torah and actions because the mouth is "Kodesh Kodashim.”