“And when a battle will come… and you shall blow the trumpets!” “And you shall blow the trumpets over your burnt offerings and peace offerings!” (Bamidbar 10:9-10)
It is a positive commandment to blow the trumpets in the temple every day, at the time of offering each offering, and also at a time of trouble, as it says “And when a battle comes in your land against an oppressor who is oppressing you, and you shall blow the trumpets and be remembered before Hashem your G-d and you will be saved from your enemies!”, and it also says “And on the day of your happiness and your festivals and the beginning of your months you shall blow the trumpets over your burnt-offerings and your peace-offerings!”.
Even though the verse stresses that one should blow on the day of happiness, and festivals etc., this is not exclusive, as they blew every day in the temple.
Amongst the roots of this commandment is that at the time of the offering of the offering the priests needed to concentrate properly, as is well-known that an offering can be condemned by the wrong intentions, and the offering also needs to have the full concentration before Hashem, who commanded us to bring it. Similarly, at a time of trouble a person needs tremendous concentration when he beseeches Hashem to have pity on him and save him from his troubles. We have therefore been commanded to blow the trumpets at these times, as since a person is made of matter he needs a great arousing to these things, as the natural way of a person is to be asleep, and is well-known that there is nothing which can awaken a person like the sound of tunes, and trumpets most of all, as that is the greatest noise amongst the musical instruments.
Another achievement of the blowing of the trumpets is that with the sound of the noise a person will remove from his heart all the other preoccupations of the world, and not give any attention at that time to anything other than the bringing of the offering, as is known to anyone who has listened to the sound of horns and trumpets.
Amongst the laws of this commandment are the trumpet must be made from one piece of silver as is said in the Torah, and if made from any other metal, it is unfit for use.
This commandment applies when the temple was standing, to priests as it is their obligation to blow on the trumpets, as it says when the camps travelled “And the sons of Aharon will blow on the trumpets!”. If the priests transgressed this and did not blow on the trumpets at the time of bringing the offering or at a time of trouble, they have contradicted this commandment.