Num 10:1-10 The LORD spoke to Moses, saying, “Make two silver trumpets. Of hammered work you shall make them, and you shall use them for summoning the congregation and for breaking camp. And when both are blown, all the congregation shall gather themselves to you at the entrance of the tent of meeting. But if they blow only one, then the chiefs, the heads of the tribes of Israel, shall gather themselves to you. When you blow an alarm, the camps that are on the east side shall set out. And when you blow an alarm the second time, the camps that are on the south side shall set out. An alarm is to be blown whenever they are to set out. But when the assembly is to be gathered together, you shall blow a long blast, but you shall not sound an alarm. And the sons of Aaron, the priests, shall blow the trumpets. The trumpets shall be to you for a perpetual statute throughout your generations. And when you go to war in your land against the adversary who oppresses you, then you shall sound an alarm with the trumpets, that you may be remembered before the LORD your God, and you shall be saved from your enemies. On the day of your gladness also, and at your appointed feasts and at the beginnings of your months, you shall blow the trumpets over your burnt offerings and over the sacrifices of your peace offerings. They shall be a reminder of you before your God: I am the LORD your God.”
Here are directions concerning the public notices to be given the people by sound of trumpet. Their laws in every case were to be Divine, therefore, even in this matter Moses is directed. These trumpets typify the preached gospel. It sounds an alarm to sinners, calls them to repent, proclaims liberty to the captives and slaves of Satan, and collects the worshippers of God. It directs and encourages their heavenly journey; stirs them up to combat against the world and sin, encouraging them with the assurance of victory. It leads their attention to the sacrifice of Christ, and shows the Lord’s presence for their protection. It is also necessary that the gospel trumpet give a distinct sound, according to the persons addressed, or the end proposed; whether to convince, humble, console, exhort, reprove, or teach. The sounding of the trumpet of the gospel is God’s ordinance, and demands the attention of all to whom it is sent. (Henry)
Before we can obey God, we must first give Him our attention. The trumpets were used to get the attention of the people of Israel. The trumpets only worked effectively with the evidences of God’s presence (the trumpets told them to start marching, but the pillar of cloud or pillar of fire showed them where to go). (Guzik)