The Parshios of Tazria and Metsora discuss in length the spiritual malaise of tzoraas whereby a person is afflicted with white blotches on his skin. He must then experience a period of isolation and finally undergo a process of purification. Chazal tell us that this affliction comes about because of a person's sins, in particular that of lashon hara (negative speech). The process that the metsora must undergo is intended to demonstrate to him the destructiveness of his sin and teach him how to improve himself in the future so that he avoid sinning in such a way again.
It seems that there are two lessons in particular that one who speaks lashon hara is taught during the period of his tzoraas: Firstly, Chazal tell us, "he caused separation between man and his friend [through his lashon hara] and therefore the Torah said that he must sit alone." Speaking negatively about others inevitably causes friendships to break apart and people to distance themselves from each other. Therefore, measure for measure, one who speaks lashon hara is forced to live alone for a period of time, separated from others. This teaches him the pain that he causes by breaking up relationships. Secondly, the blotches themselves act as a potent demonstration of the damage that one who speaks lashon hara does to his neshama (soul). Tzoraas is not a regular physical illness, rather it is the physical manifestation of a spiritual malaise that offers indisputable evidence to the sinner that he has greatly damaged himself in a spiritual sense and is in desperate need of spiritual improvement.
Nowadays there is no tzoraas, and superficially this may seem like a good thing. However, the commentaries point out the exact opposite; tzoraas was a chessed (kindness) of Hashem in that He communicated very clearly to the sinner of his transgression and the need to do teshuva. Without this gift, it is immeasurably more difficult for a person to recognize when he has sinned. And yet, it is very clear that the sin of lashon hara remains as one of the most difficult to avoid. Indeed the Gemara writes that whilst a minority of people stumble in arayos, and a majority stumble in certain forms of theft; "everyone [stumbles] in avak lashon hara." Given the apparently widespread transgression of lashon hara, what replacement is there for tzoraas - how can a person recognize the spiritual damage one causes himself when he speaks lashon hara and the extent of the damage that negative words can have on other people?
Rav Alexander Moshe Lapidus in his sefer, Divrei Emes answers this question. He notes that a person who had tzoraas had to go to a Kohen who would guide him through the process of teshuva. Now, there remains a Kohen who continually guides us how to rectify the sin of lashon hara - that is the Chofetz Chaim zt"l, whose sefarim on this topic are the ultimate authorities in the laws and Torah outlook about guarding ones speech. They teach a person about the damage he causes other when he speaks lashon hara and they show at length the harm that one who speaks lashon hara does to himself. The Chofetz Chaim himself writes in the name of the Maharsha, that when the Gemara says, everyone sins in avak lashon hara, it refers to everyone who does not make a conscious effort to improve his speech. However, if a person learns the laws and outlook about guarding one's speech then he will be able to avoid this pernicious sin. Whilst nobody in this generation is afflicted with tzoraas, it is apparent that everyone who does not work on himself in this area will inevitably speak at least avak lashon hara. Thus, the insight of the Divrei Emes teaches us that it is incumbent upon everyone to learn about the laws of lashon hara from the Chofetz Chaim.
One still may ask, why is it necessary to learn the laws of lashon hara, wouldn't it be sufficient to learn mussar about the damage it does, and thereby one would develop enough yiras Hashem (fear of Hashem) to avoid speaking lashon hara. The Chofetz Chaim addresses this issue in his introduction to his mussar sefer, Shemiras Halashon. He writes that it is not sufficient to learn this work alone, rather one has to also learn his halacho sefer, Chofetz Chaim: "What is the benefit of all the mussar in the world that speaks of the severity of the prohibitions of lashon hara and rechillus, since he has permitted himself saying that this thing is not included in lashon hara, or that the Torah did not prohibit speaking lashon hara about this kind of person, therefore one must know which things do fall in the category of lashon hara." Thus, the Chofetz Chaim teaches us that without knowing the laws of lashon hara a person will inevitably stumble because he is not aware what constitutes forbidden speech.
A second reason for the importance of learning the laws of lashon hara can be derived from a teaching of Rav Yisroel Salanter: He taught that learning about a particular area of halacho is an excellent way of developing an awareness of ever stumbling in that specific area. Accordingly, when he would find himself in a situation that could potentially lead to transgression of yichud he would immerse himself in learning about it, thus ensuring that he would maintain constant vigilance in this area. In a similar vein, one Rav who taught beginners the laws and hashkafa of Shabbos, noted that far more people began keeping Shabbos as a result of his halacho classes than from those in hashkafa. He explained that when a person is learning about the laws of a melacha, it is far more difficult for him to blatantly transgress that very melacha on the following Shabbos. Similarly when a person is constantly learning the laws of lashon hara he is far more likely to be able to maintain awareness of his speech and ensure that he speaks no forbidden words.
Based on the constant test of speaking lashon hara and the Gemara's assertion that no one is free from this sin, it seems that the only way to improve in this area is through constant study of the laws and hashkafa of shemiras halashon (guarding ones speech). Accordingly, many Gedolim signed a document urging everyone to set aside a time to learn both Sefer Chofetz Chaim and Sefer Shemiras Halashon. Moreover, they instructed every institution head to try to include classes about guarding ones speech in the regular learning schedule. In this vein, the Manchester Rosh Yeshiva, Rav Yehuda Zev Segal zt"l developed a daily calendar for learning these two sefarim, and shortly before his passing, he asked the Chofetz Chaim foundation to produce the sefer, 'A Lesson a Day' which constitutes a short daily section on halacho and hashkafa. These Gedolim recognized that constant learning about shemiras halashon was the only way to ensure avoiding transgressing the severe prohibition of lashon hara.
In earlier times, one who spoke lashon hare was inflicted with tzoraas and guided by the Kohen in his teshuva process. Now, a person is not blessed with such a clear message, and therefore, and he must turn to the words of the great Kohen, the Chofetz Chaim to guide himself how to improve his speech through constantly learning his great sefarim. May we all be blessed with the ability to avoid all forms of negative speech.
 Arachin, 15b-16a.
 Arachin, 16b.
 See Rav Shimshon Raphael Hirsch zt"l who proves at length that tzoraas is not the same as the physical sickness of leprosy.
 Translated as immorality.
 Bava Basra, 165a. Avak literally means 'dust'. Avak lashon hara is known as the 'dust' of lashon hara in that it does not constitute the Torah prohibited lashon hara, but it represents a number of forms of speech that are forbidden by the Rabbis because of their resemblance to lashon hara or their likelihood in leading one to speak the lashon hara that is prohibited by the Torah. See Sefer Chofetz Chaim, Hilchos Lashon Hara, Klal 9 for a thorough outline of avak lashon hara.
 Quoted in Lekach Tov, Parshas Tazria, p.107.
 The sefer, Chofetz Chaim discusses the laws of lashon hara and Shemiras Halashon outlines the Torah's outlook about lashon hara.
 Shemiras Halashon, Ch.15.
 The word, 'mussar' is usually translated as growth, although the root of the word comes from the same root as yissurim, which means suffering, teaching that the process of self-growth can be a painful one.
 'Rechillus' is another form of prohibited speech in which Reuven informs Shimon of how Levi spoke badly about Shimon, thus causing great damage to their relationship.
 Introduction to Shemiras Halashon, p.17.
 Yichud (literally meaning alone) is the prohibition to be alone with a member of the opposite gender in certain circumstances.
 A creative form of activity that is prohibited on Shabbos.
 Including, Rav Chaim Shmuelevitz zt"l, The Steipler Gaon zt"l, the Beis Yisroel zt"l, Rav Wosner Shlita and many others.
 Including the Rav of a community, a head of a Yeshiva katana or a head of a Seminary.
 Kriah Gedolah found at the beginning of 'A Lesson a Day'.
 Also found at the beginning of 'A Lesson a Day'.