In Exodus 19:13; 20:18; Joshua 6:5, 20; 1 Samuel 13:3; Psalm 47:5; Isaiah 18:3; Matthew 6:2; Revelation 1:10; 8:2, trumpets signify celestial good, because the sounds of musical instruments correspond to affections for truth and good, and wind instruments to the latter. (Arcana Coelestia 8802)

The sounds of trumpets are heard in heaven when assemblies and appointments happen. So among the children of Israel, for whom everything was representative of heaven and the church, it was also commanded that they should make trumpets of silver, and that the sons of Aaron should blow them to call assemblies, when the camps set out on journeys, in days of celebration, in festivals, at the beginning of months, over burnt-offerings, for memorials, and going to war, as in Numbers 10:1-11. 'Seven trumpets' which the seven angels sounded in Revelation 16, signify the exploring and exposing the falsities and evils when people are in faith separate from charity. 'To sound a trumpet,' regarding its effect, signifies the revelation and manifestation of divine truth, and in the opposite sense, the deprivation of truth and desolation. 'Sounding with trumpets' signifies calling together on solemn occasions, and also exploring and discovering the quality of the church.

(Reference: Apocalypse Revealed 226)

226. And the first voice that I heard was like a trumpet speaking with me, saying, "Come up here." This symbolizes a Divine influx, resulting in an elevation of the mind and consequent clear perception.

When a voice is heard from heaven, it means Divine truth flowing in (see nos. 37, 50 above), thus a Divine influx. And a voice like a trumpet symbolizes a clear perception (see again no. 37 above). "Come up here," moreover, symbolizes an elevation of the mind, for in the spiritual world, the higher one ascends, the purer the light that he comes into, by which the intellect is progressively opened or the mind elevated. Consequently the statement also follows that John was then in the spirit, meaning that he was conveyed into a spiritual state, in which the things found in heaven clearly appear.

The voice sounded like a trumpet because the subject is the organization of the heavens for a last judgment. Moreover voices like trumpets are heard in heaven when assemblies and organizations are taking place. Consequently in the case of the children of Israel also, with whom everything was representative of heaven and the church, it was a statute that they make trumpets of silver, and that the sons of Aaron sound them to assemble the congregation; to decamp; on days of celebration; at festivals; at the beginnings of months; upon the offering of sacrifices; as a memorial; and to go to war (Numbers 10:1-10).

But we shall speak of trumpets and the sounding of them in our exposition of chapter 8, where the subject is the seven angels who were given seven trumpets.