If you go to war in your land against an adversary that attacks you, you must blow a teruah with the trumpets and be remembered [favorably] before G-d, your G-d, and thus be saved from your enemies.
On the joyous days, on your festivals, and on your new-moon celebrations, you must blow on the trumpets over your ascent offerings and your peace-offerings, and it will be a remembrance before your G-d.
Bemidbar 10:9-10
Allegorically, the war we are constantly fighting is the war against our evil inclination. This fight is particularly intense during prayer, when the evil inclination tries to distract us from concentrating on G-d and deepening our relationship with Him.
The allegorical "trumpet" we sound in order to enlist G-d's help against the evil inclination is our heart-broken cry, the silent tears we shed over being so spiritually weak that we are vulnerable to the evil inclination's strategies. When we beseech G-d to have mercy on us, He comes to our aid and rescues us from our enemy.
But we see here (verse 10) that we must blow the trumpets not only while in the thick of battle, but also when we have overcome the enemy, and even on joyous festivals.
Blowing the trumpets on these occasions reminds us that our victory over the evil inclination is never final and we should never let our success get the better of us. The evil inclination is always devising new ways to ensnare us, and we must be constantly on guard, constantly enlisting G-d's help and mercy.
The sacrifices mentioned here reflect the two basic stages in how we approach G-d. (As we have seen, "drawing close" to G-d is the true meaning of the Hebrew word for "sacrifice," korban.)
The first stage is the ascent-offering, whose meat and fat is totally consumed on the Altar. First, we must submit ourselves totally to G-d. The second stage is the peace-offering, part of whose meat is eaten by those who offer it. After we have established the basis of total submission to G-d, we can (and should) enhance our relationship with Him and His will as we can, igniting our enthusiasm for the Torah and its commandments.
In our daily lives, the dynamic of the ascent-offering is expressed in our morning prayers, the basis for the rest of the day. In prayer, we surrender our sense of self and cling devotedly to G-d. The dynamic of the peace-offering is expressed as we pursue our personal affairs throughout the day, always bearing in mind that all we do must be done for the sake of heaven and in order to enhance our Divine consciousness.
--From Kehot's
Chumash Bamidbar