Daf Yomi - Yoma 43 - Torah Says it Anyway

The Gemora brings a rule - מילתא דאתיא בקל וחמר טרח וכתב לה קרא - something that can be learned from a kal v'chomer, the Torah will write it anyways. What is the rationale behind this? The Bnei Yisoschor explains that all droshos that are learned out are halacha l'Moshe misinai and they might not have any logical reason behind them and they are accepted. A kal v'chomer could be understood. It makes logical sense. One might mistakenly think that the halacha is true when learned with a kal v'chomer because he understands it. The Torah shows us that this is not the case. Even though it makes perfect sense and self explanatory without the Torah explicitly expressing it, nevertheless, the Torah writes the halacha down to illustrate to us that it is because of the Torah that this halacha is true.

There are Rishonim however, that apply this concept by a gzeira shova, as well. Tosfos in Shabbos applies it by a ma hatzadand there are others that relate it to a binyon av. All of these methods of droshos are not understood with logic, but yet the Torah finds it necessary to state those halochos.