Numbers 10:9

If ye go to war in your land— Bishop Patrick observes, that as these trumpets were to be used in summoning the armies of Israel to go forth to battle; so, previously to that, in calling the people together to implore a blessing upon their arms; as the latter part of the verse intimates, and as it is explained by Maimonides and other ancient interpreters: which exposition is confirmed by the prophet Joel, ch. Numbers 2:1; Numbers 2:15 where, at the same time that the alarm of war is ordered to be sounded, a fast is ordered to be proclaimed by blowing the trumpet.

And ye shall be remembered before the Lord— Continues the sacred historian: the sounding of the trumpets being a kind of call upon God to assist them, and a sign to the people to implore and rely upon the divine aid:—that they may be to you for a memorial before your God, Numbers 10:10 see Psalms 150:3. In 2 Chronicles 13:14 we read, that Judah, seeing themselves beset with dangers before and behind, cried unto the Lord, and the priests sounded with the trumpets; and it is here promised, that if they do so, [no doubt, a true repentance, is implied] they should be saved from their enemies.