There is an interesting contrast between the language used when Hashem instructed Noach to take the animals with him into the ark, and that which is used in our parsha when explaining the laws of kashrus. Regarding Noach the Torah says ”and of the beast that is not-clean, two” (Bereishis 7:2). The scripture uses a non-derogatory term ”not-clean” for the impure animals, effectively adding letters to the Torah, yet in our parsha it refers to these animals as ”tamei”, ”unclean” a shorter form. How can we account for this difference? The Dubno Maggid cites a parable. In a certain town lived two people both called Yosel. One was a wise man, well versed in Torah, whilst the other was completely ignorant, and was known as Yosel the Boor, to distinguish him from the other. One day a man came to the house of the learned Yosel and asked his servant if he knew where the other Yosel could be found. The servant replied ”You mean Yosel the Boor?” When his master heard him talking like that he reprimanded him ”You must not call any man a boor, people only call him that to distinguish us, but in my house there is no excuse for this, I will not have people think I look down on one of my neighbours”. A while later a shadchan came to the scholarly Yosel, suggesting a shidduch between his daughter and the son of the ignorant Yosel. Yosel was furious at him even for suggesting it; ”My daughter, married to the son of Yosel the Boor, not while I’m alive”. After the shadchan left the servant asked his master why a while earlier he had been told off, yet the master himself had used such uncomplimentary terms. Yosel explained the difference. ”If someone asks you where someone lives, you are not required to give any information about his character, simply giving the address will do. When I receive a marriage proposal for my daughter, I have to be straight and to the point why I object. It is my duty to explain to the shadchan that my daughter will not marry the son of one who is known for being an ignoramus.” The same applies in the Torah. With Noach, the impure animals were being listed only for the purpose of information, to identify who should and shouldn’t go into the ark. Therefore it was sufficient to use the terms clean and not-clean. In our parsha, the laws of kashrus are set out and a line is being drawn between what is and what isn’t permissible. Yisroel has a special status and has to retain holiness, therefore the Torah has to be blunt and call the non-clean animals what they are; tamei.
A student once asked Rav Elchonon Wasserman why he used such harsh words for those he held to be wicked. He asked; “surely if the Torah used extra letters (as above) in order to avoid impure expressions, surely it would oblige the Rabbi to do so, with all due respect?” Rav Elchonon answered with the above idea, that when the Torah wanted to tell Yisroel which animals were fit to be eaten, it calls them “impure” without trying to use a nicer expression. So too, when it is time to defend the faith against the destroyers and underminers of religion, there is no reason to try and be more polite. He is quoted as saying “This is especially true at a time when there are those who seek to purify that which is treif. It is obligatory to point out that the Torah considers them impure.”