Don't Defile Yourself

אֱמֹ֥ר אֶל־הַכֹּהֲנִ֖ים בְּנֵ֣י אַהֲרֹ֑ן וְאָמַרְתָּ֣ אֲלֵהֶ֔ם לְנֶ֥פֶשׁ לֹֽא־יִטַּמָּ֖א בְּעַמָּֽיו

Why the double terminology of אמר ואמרת? Why does the possuk switch from speaking to the klal to speak to the individual לא יטמא, it should have said לא יטמאו? Why does it say לנפש לא יטמא and not למת לא יטמא? Why does it say בני אהרן, we know the kohanim are the offspring of Aharon? The Chassidishe seforim understand this possuk is not just a halacha to kohanim not to defile themselves to the dead but the Torah is a also giving a command to everyone not to defile themselves with things that will contaminate their soul (see Toldot Yaakov Yosef, Mey Hashiloach etc. that develop the possuk according to their explanation.) The first command, אמור אל הכהנים is a general command not to defile one's self. This refers to things which defile everyone and there is a general warning for everyone to avoid those activities. L'havdil that is like the warning on a cigarette package that the product inside will likely cause harm. Who should teach about taharah, how to avoid defilement? Kohanim בני אהרן, those that are attached to Aharon, who achieved this level of purity (see the Midrash begging of the parsha about the yirat shamayim of Aharon and Sfas Emes 5652,) and can teach it to the klal.  ואמרת אלהם, another command, לנפש לא יטמא, one should not defile their own nefesh. Everyone has their own path with the things to avoid because they will harm the individual in their service of Hashem. There maybe things which do not affect one person but cause harm for another individual. That is like the warning on medications that they could be good for some people but for people taking other mediations or other complications, the medication can be very harmful.  The Torah warns one must be careful to avoid things which are harmful for one's own nefesh (see Toldot, Emrei Emes 5683.)