And that is that He commanded us to blow with trumpets in the Temple during the bringing of the holiday offerings. And that is His, may He be exalted, saying, "And on your joyous occasions and on your festivals [...], you shall blow, etc." (Numbers 10:10). In the explanation (Rosh Hashanah 26b), they said that this commandment (on public fasts) is with the trumpets. And the regulations of this commandment were already explained in the Sifrei, in Rosh Hashanah and in Taanit. And likewise are we commanded to blow with trumpets at times of need and of distress, when we yell out in front of God, may He be exalted. And that is His saying, "When you are at war in your land against an aggressor who attacks you, etc." (Numbers 10:9). (See Parashat Behaalotecha; Mishneh Torah, Fasts 1.)