Kommentar zu Bamidbar 10:7

ובהקהיל את הקהל וגו׳ AND WHEN THE CONGREGATION IS TO BE GATHERED TOGETHER etc. — Because it is stated, (v. 2) “and they shall be unto thee for calling together the assembly and for the journeying of the camps”, you must reason as follows: How is it in the case of “the calling of the assembly”? A Tekiah was made by two priests and on both of them (on two trumpets), since it states, (v. 3) “when they blow with them (cf. Rashi on that verse). So, too, is the setting out of the camps to be by means of both trumpets. One might, however, also reason as follows: How is it in the case of the “journeyings of the camps”? The priest sounds a Tekiah, a Teruah, and another Tekiah (cf. Rashi on v. 5)! So, too, in the case of “calling the assembly together”, he blows a Tekiah, a Teruah and a Tekiah, so that it follows that there is no difference between the signal for “calling the assembly” and that for the “journeyings of the camps”. Scripture, however, states here: “And when the congregation is to be gathered together, etc.” to intimate that no Teruah is sounded at the calling of the assembly (ולא תריעו), and the same rule applies to calling the princes. — Thus we have a different signal for the three occasions: “the calling of the assembly” is done by both trumpets, and that of the princes by one — but neither in this nor that signal is there a Teruah, whilst “the journeying of the camps” is done by both trumpets with a Teruah, a Tekiah preceding and following it (Sifrei Bamidbar 74).

Since it says. Rashi is answering the question: Firstly the Torah already writes above “you shall blow and you shall present yourselves…” Furthermore from where would one learn a requirement for a tekiah, teruah, tekiah such that it had to write “you shall blow [a tekiah] but not a teruah.” He answers “since it says, ‘They shall be used by you…’”

ובהקהיל את הקהל, “but when the assembly is to be called together, etc.” on this verse Rashi comments: “seeing that we might have thought that seeing that the construction of the trumpets had been introduced as something that Moses was to do personally, and use by himself, that just as for breaking camp there would be a blast of tekiyah followed by a blast of t’ruah, followed again by a blast of tekiyah, the same would be the signal for a general assembly; However, if that were so how would the people have known the significance of these blasts? In order to prevent such a misunderstanding, the Torah in our verse specifically warns that when the trumpet call served to call the people to an assembly there would not be the alarming blast of the t’ruah.”

Perhaps, just as, when initiating the camps’ departure. Since the two are compared together, one might have said that ‘just as when initiating the camps’ departure…” therefore it was necessary to exclude this.