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Parshat Tzav includes a Passuk (verse) scarcely commented on, describing how the Kohen (Priest) needs to remove the clothes he wore when he gathered the ashes of the Olah offering, put on "other clothing" (6:4) and remove the ashes. Why would a change of clothing be required for simply walking ashes?

Rashi explains that it's not proper to mix a cup of wine for one's superior in the same clothing in which one cooked a pot. Rav Moshe Feinstein points out how the Torah considers the rules of proper decency and etiquette so important that it included laws to that effect in the Torah. Being decent and acting properly isn't just a good idea, it's the law!