Commentaire sur Les Nombres 15:38

That is that He commanded us to make tzitzit (fringes). And that is His, may He be exalted, saying, "to make for themselves fringes [...] let them attach to the fringe at each corner" (Numbers 15:38). And [the two colors of strings are] not counted as two commandments, even though the main understanding for us is that the blue-purple does not impede the white and the white does not impede the blue-purple. For it is said in the Sifrei, "It is possible that they are two commandments, the commandment of the white and the commandment of the blue-purple. [Hence] we learn to say (Numbers 15:39), 'That shall be your tzitzit' - it is one commandment and not two commandments." And women are not obligated in it, as is explained in the first [chapter] of Kiddushin (Kiddushin 33b). And the regulations of this commandment were already explained in the fourth chapter of Menachot. (See Parashat Shelach; Mishneh Torah, Fringes 1.)

ועשו להם ציצת THAT THEY MAKE THEM A FRINGE — It is called צצית, because of the threads that hang down from it. Similar is, (Ezekiel 8:3) “and he caught me by the curls (ציצת) of my head’’. (The word denotes something twisted as threads or curls). — Another explanation is: it is called ציצת because of the command associated with it (v. 39) “and ye shall look at it”. Similar is, “looking (מציץ) from the lattice” (Song 2:9). (The word therefore denotes “something looked at”) (Sifrei Bamidbar 115).

Speak etc. and you shall say: Since there is an element of commandment as well as advantage, and honor which come from the commandment, therefore it said both Speaking (in a commanding form) and saying (in a gentle and respectful form).