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; 2Ch 13:12, 2Ch 13:14; 2Ch 20:21-22, 2Ch 20:28) as well as on joyful occasions, such as at the removal of the ark (1Ch 15:24; 1Ch 16:6), at the consecration of Solomon’s temple (2Ch 5:12; 2Ch 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 (2Ch 29:27).