Numbers 10:8-10

8The sons of Aaron, the priests, will blow the trumpets. This will be a permanent law for you and your descendants.

9“When you go to war in your own country against an enemy who is oppressing you, the trumpets will sound a fanfare. Then the Lord your God will remember you and rescue you from your enemies.

10Also, on your festival days and on the first day of the month, blow the trumpets when you sacrifice your burnt offerings and fellowship offerings. The trumpets will be a reminder for you in God’s presence. I am the Lord your God.”