Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

These trumpets were to be used for the holy purposes of the congregation generally, and therefore not only the making, but the manner of using them was prescribed by God Himself. They were to be blown by the priests alone, and "to be for an eternal ordinance to the families of Israel," i.e., to be preserved and used by them in all future times, according to the appointment of God. The blast of these trumpets was to call Israel to remembrance before Jehovah in time of war and on their feast-days. Num 10:9 "If ye go to war in your land against the enemy who oppresses you, and ye blow the trumpets, ye shall bring yourselves to remembrance before Jehovah, and shall be saved (by Him) from your enemies." מלחמה בּוא, to come into war, or go to war, is to be distinguished from למּלחמה בּוא, to make ready for war, go out to battle (Num 31:21; Num 32:6). Num 10:10 "And on your joyous day, and your feasts and new moons, he shall blow the trumpets over your burnt-offerings and peace-offerings, that they may be to you for a memorial (remembrance) before your God." - השּׂמחה יום is any day on which a practical expression was given to their joy, in the form of a sacrifice. The השּׂמחה are the feasts enumerated in chs. 28 and 29 and Lev 23. The "beginnings of the months," or new-moon days, were not, strictly speaking, feast-days, with the exception of the seventh new moon of the year (see at Num 28:11). On the object, viz., "for a memorial," see Exo 28:29, and the explanation, p. 450. In accordance with this divine appointment, so full of promise, we find that in after times the trumpets were blown by the priests in war (Num 31:6; Ch2 13:12, Ch2 13:14; Ch2 20:21-22, Ch2 20:28) as well as on joyful occasions, such as at the removal of the ark (Ch1 15:24; Ch1 16:6), at the consecration of Solomon's temple (Ch2 5:12; Ch2 7:6), the laying of the foundation of the second temple (Ezr 3:10), the consecration of the walls of Jerusalem (Neh 12:35, Neh 12:41), and other festivities (Ch2 29:27).