Matthew 24:31

“And he will send his angels and gather his elect from the four winds, from the ends of the earth to the ends of the heavens.”

Parallel account of the gathering of the elect.

“For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first.”

Connects the trumpet call with the return of Christ and gathering of believers.

“And in that day a great trumpet will sound. Those who were perishing in Assyria and those who were exiled in Egypt will come and worship the LORD on the holy mountain in Jerusalem.”

Old Testament prophecy of a future gathering signaled by a trumpet.

“After this I looked, and there before me was a great multitude that no one could count, from every nation, tribe, people and language, standing before the throne and before the Lamb.”

Describes the great multitude gathered from all nations.

“Then the LORD will appear over them; his arrow will flash like lightning. The Sovereign LORD will sound the trumpet; he will march in the storms of the south.”

Connects the Lord's appearing with the sound of a trumpet.