From verse 1 we learn that it is a proclamation of truth that warns the people of The Day of The Lord. This trumpet is symbolic of a great proclamation of truth at Christ's return. They are common to history. The powers of the heavens shall be shaken. Drastic changes will rock the nominal church heavens.
Stars can symbolize either faithful or unfaithful teachers.
Indeed, the powers of the heavens are shaking. The battle between the fundamentalist and modernist has sorely rent the church heavens. Since Vatican II, Catholicism is also being sorely rent. One of the first evidences of Christ's parousia, presence, will appear in the nominal church heavens. It is the darkening of the sun and moon, and the fall of the stars.