Charles H. Spurgeon on Psalms 81:3

The trumpet. The sound of the trumpet is very commonly employed in Scripture as an image of the voice or word of God. The voice of God, and the voice of the trumpet on Mount Sinai, were heard together (Ex 19:5,18-19), first the trumpet sound as the symbol, then the reality. So also John heard the voice of the Lord as that of a trumpet (Re 1:10 4:1), and the sound of the trumpet is once and again spoken of as the harbinger of the Son of Man, when coming in power and great glory, to utter the almighty word which shall quicken the dead to life, and make all things new (Mt 24:31 1Co 15:52; 1Th 4:16). The sound of the trumpet, then, was a symbol of the majestic, omnipotent voice or word of God; but of course only in those things in which it was employed in respect to what God had to say to men. It might be used also as from man to God, or by the people, as from one to another. In this case, it would be a call to a greater than usual degree of alacrity and excitement in regard to the work and service of God. And such probably was the more peculiar design of the blowing of trumpets at the festivals generally, and especially at the festival of trumpets on the first day of the second month. Joseph Francis Thrupp.