Musar su Isaia 51:6

Now we shall explain the greatness of the merit of one who guards his mouth and his tongue from speaking forbidden things. First, he amends and sanctifies thereby the distinctive "tool" of the Jew, which is speech. So that all the words that he speaks thereafter in Torah and in prayer ascend to the source of its root on high. For not in vain did Chazal compare this [faculty] in many places to a "tool of the trade" [see Rashi, Bamidbar 31:8], to teach us that just as a tool is necessary for the making of new, beautiful vessels, [so is it with the "tool" of speech]. Even if one be the king's craftsman, the greatest of all the artists, whose intellect is extremely subtle, and who can conceive of the finest way of fashioning vessels, still, he cannot make them without tools. And, more than this, even if he has the tools, but they are defective and damaged, and he is "pressured" to make some vessels, there will be recognized through them the defect and the imperfection of the tools, inside and outside, because he will not be able to smooth them [the vessels] out correctly and they will remain like formless blocks of wood, unfit for use even by commoners; how much more so, for a king. But that craftsman whose tools are polished and shined as they should be — the vessel that he fashions with them will emerge perfect and beautiful. It is exactly the same with the faculty of speech given to the Jew for the service of the awesome King (blessed be His name) for Torah and prayer, and for blessing, glorifying, praising, and exalting Him. For it [(this faculty)] is the great tool whereby the complete man can build heaven and earth, as it is written (Isaiah 51:6): "And I have placed My words in your mouth to plant the heavens and to lay the foundations of the earth." And this is to be understood literally. For with the words of holiness that a man speaks here in this world before the blessed L-rd, there are created on high holy worlds and angels, who will afterwards be protagonists for and defenders of his soul. And the quality of the worlds and the angels created through his Torah and mitzvoth depend on several factors: 1) his mind-set at the time. That is, his having readied himself at that time with all his powers to fulfill his task according to the Torah, in all of its requisite parts and details. 2) his tools, by which his Torah is fashioned. That is, the tools of speech (and, likewise, in respect to the mitzvah, the tools required to execute it.) For if they are beautiful and elegant, being used always for the good, and the power of their sanctity being thereby strengthened, they will have the power to draw down the higher sanctity and great light on whatever he is doing. But if he renders defective and unclean, G-d forbid, his faculty of speech through lashon hara, rechiluth, levity, and falsity, and the like, and he does not repent, and then he speaks with his mouth words of Torah and prayer, what power will they have to draw down on that Torah and prayer the higher sanctity after his "tools of utterance" have been rendered defective and unclean in and of themselves?

The Tziyoni writes in a gloss on פרשת בראשית that the reason we are to be so careful with observing the details of the legislation of צרעת, blemishes of the skin, the clothes, or the house, is that we are dealing here with inner blemishes, i.e. sins, which have become visible externally. G–d has been very kind in externalizing the effect of these sins so as to give the afflicted person an opportunity to repent and rid himself of the pollutant of the serpent which his sins are due to. The priest is the only one who can effect a cure because the priesthood originated in the "right" side of the diagram of emanations in the emanation חסד, whereas the pollutant of the serpent has its origin in the "left" of the diagram of emanations, the side from which Samael originates. Nowadays, when we do not have priests who can perform the steps leading to the rehabilitation of an afflicted person (including the sacrifices he has to bring at the end of the period of his isolation as outlined in Leviticus 14,2-32), repentance is the only instrument by which we can cleanse ourselves. The right hand of G–d is always stretched out to welcome penitent sinners.