Responsa su Numeri 15:38

This can be understood as an a priori argument from the techaylet of tzitzit¹⁸⁷Techailet is the special blue dye (made from the tropical sea snail murex trunculus) for the wool fringe of the tzitzit which is a biblical requirement (Num. 15:38) of placing fringes on any four-cornered garment, in this case of linen, with one wool fringe., which the Torah was very specific about and quite stringent in its method of production¹⁸⁸See Tractate Menachot 42b-43b. Despite that one places various chemicals into the blood of the khilazon (Murex snail) as explained in tractate Menachot 42b¹⁸⁹See the appendix. The Tosafot wrote, loc. cit. ‘Ingredients (chemicals)’ were indeed perplexed by this and wrote that perhaps those chemicals could be [part of what is] called ‘techaylet’- the blue-ish dye.

They responded: "O Generation! See the word of God!" "Why do you argue about Me? You have all sinned before me!" (Jeremiah 2:29-31) They explained their words as follows: "O Generation" - are you as the generation who crossed the desert, which argued about the techelet dye?³See Midrash Tanchuma, Korach 2, quoted by Rashi on Numbers 16:1 Why then do you argue then about wool and linen? "You have all sinned before me!" - for neither will wool nor with linen [techelet threads] do you come. "See the word of God!" - See what is written in the Torah. Does is not say "see... and recall... and perform" (Numbers 15:39)? The time of performing this commandment of tzitzit is the entire day ⁴i.e, throughout the daylight hours, when one can 'see'., yet you rid yourself of this obligation after a single hour. The early pious ones are testimony to the habit of not walking even one moment without wearing tzitzit. All this they truly responded to me, and my heart was disturbed over this response. I gathered my strength and asked again before the King, that he might instruct them to inform me whether a woolen tallit is more acceptable than a linen one, or whether they are equal, or whether linen is invalid. They responded: the halacha is well-established among us that wool and linen are equal, and for each one, the threads are valid for the garment of that type. The reason comes from what is written (Numbers 15:38) "They shall make for themselves tzitzit on the corners of their garments." Why does it specify 'for themselves'? It means that any garment that is common among them. For the Torah does not want to be oppressive and require something that not everybody has. Rather, it allows whichever of these two materials their garment is made of, wool or linen. Some time later they responded again: "It is because of the anger replaced in our bags, to make us roll and to condemn us." (cf. Genesis 43:18) They were precise about this word 'anger', spelling it out to me ⁴The original verse has the word 'kessef', money, while here they say 'ketsef', anger. They explained that the Great King is angry with us on this matter of tzitzit, that we should have paid attention to and have worn it on the corners of our garments. Now we are being brought to the Day of Judgement, 'to make us roll and condemn us'.