Siman 19

It has already been explained that the mitzvah of tzitzit is not an obligation like tefillin and mezuzah, for if one does not have a four-cornered garment, he is exempt from this mitzvah except when he has one. And even in this, they disagree in Menachot (42b) whether it is an obligation of the tallit, meaning that when he has a four-cornered garment, even if it is placed in a box, it is obligated in tzitzit; or specifically an obligation of the person, meaning when he wears it, then it is obligated in tzitzit, but when he does not wear it, it is exempt. And there is a practical difference also regarding the matter of the berakhah, for we hold that every berakhah over a mitzvah must be recited at the time of the completion of the mitzvah. Therefore, if it is an obligation of the tallit, one must recite the berakhah "...who has sanctified us... to make tzitzit," for that is the completion of the mitzvah. But if it is an obligation of the person, then the mitzvah is at the time he wears it, and he recites then "on the mitzvah of tzitzit" or "to wrap oneself in tzitzit." And so we hold, that it is an obligation of the person, and the berakhah is at the time of the wearing and the wrapping (ibid.). (And it seems to me that if it were an obligation of the tallit, he would only need to recite the berakhah one time.)

And there is a question regarding this: Behold, mezuzah is also an obligation of the resident, and if a person does not reside within it, he is exempt from mezuzah. Nevertheless, we hold in Yoreh Deah siman 289 that he recites the blessing at the time he fixes it to the entrance, and not at the time he enters to reside in it (Magen Avraham subsection 1). And it must be said that because with mezuzah, he presumably resides in it immediately, which is not the case with a tallit (ibid.). For even if he does not yet reside in it, in any event, he presumably brings some household vessels there, and it is likewise obligated in mezuzah, as is explained there in siman 286. And according to this, there would be grounds to say that if he is wearing his tallit and its tzitzit were severed, that when he makes the tzitzit and immediately wears it, he should recite the blessing "to make tzitzit" just as with mezuzah "to fix a mezuzah" (ibid.). However, in truth it is not comparable, for behold, with a tallit, when the tzitzit become invalid, he is obligated to remove the tallit immediately, which is not the case with a mezuzah when it becomes invalid—they did not trouble him to uproot his residence (ibid.). Furthermore, regarding the essence of the matter, it is not comparable, for certainly if the blessing on tzitzit were only once at the time of the beginning of the mitzvah and no more, like with mezuzah, we could well recite the blessing at the completion of its making, and we would not be exacting as to whether he wears it immediately or not. But with tzitzit, behold, he must recite the blessing every time he wears it, since it is an obligation of the person and not an obligation of the tallit. Therefore, it is impossible to change the blessing from the first time to other times. (And in Menachot ibid. where they said to recite the blessing at the completion of its making—this is according to the one who says it is an obligation of the tallit, see there. Examine it and you will find it simple.)

If one made a tallit for the purpose of his shrouds, even though he wears it sometimes during his life – it is exempt from tzitzit, for this is like a garment of the night which is exempt even during the day according to the method of the Rosh. And even according to the Rambam, it is because this is not called "your garment" at all, as it is not a garment of the living (Beit Yosef). And there are those who hesitate, saying that according to the method of the Rambam when he wears it – he is obligated in tzitzit (Magen Avraham subsection 2). And in the Gemara they only said this according to the one who holds it is an obligation of the tallit, see there (in Menachot 41a).