C. F. Keil and Franz Delitzsch on Numbers 10:8

Num 10:8

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.