תקיעה בחצוצרות בשעת מלחמה - חזרה למצווה נשכחת

(9) When you are at war in your land against an aggressor who attacks you, you shall sound short blasts on the trumpets, that you may be remembered before your God יהוה and be delivered from your enemies.

(8) The trumpets shall be blown by Aaron’s sons, the priests; they shall be for you an institution for all time throughout the ages. (9) When you are at war in your land against an aggressor who attacks you, you shall sound short blasts on the trumpets, that you may be remembered before your God יהוה and be delivered from your enemies.

(1) It is a positive Torah commandment to cry out and to sound trumpets in the event of any difficulty that arises which affects the community, as [Numbers 10:9] states: "[When you go out to war... against] an enemy who attacks you and you sound the trumpets...." [This commandment is not restricted to such a limited scope; rather] the intent is: Whenever you are distressed by difficulties - e.g., famine, plague, locusts, or the like - cry out [to God] because of them and sound the trumpets.

(1) 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.)

(2) Have two silver trumpets made; make them of hammered work. They shall serve you to summon [military bodies of] the community and to set the divisions in motion.

(1) A king should not wage other wars before a milchemet mitzvah. What is considered as milchemet mitzvah? The war against the seven nations who occupied Eretz Yisrael, the war against Amalek, and a war fought to assist Israel from an enemy which attacks them. Afterwards, he may wage a milchemet hareshut, i.e. a war fought with other nations in order to expand the borders of Israel or magnify its greatness and reputation.