Charles Ellicott Commentary Isaiah 27:13

"And it shall come to pass in that day, that a great trumpet shall be blown; and they shall come that were ready to perish in the land of Assyria, and they that were outcasts in the land of Egypt; and they shall worship Jehovah in the holy mountain at Jerusalem." — Isaiah 27:13 (ASV)

The great trumpet shall be blown ... —The symbolism had a probable origin in the silver trumpets which were used in the journeys of the Israelites for the calling of the assembly and for the journeying of the camps (Numbers 10:1–10), and which were solemnly blown in the year of Jubilee on the eve of the Day of Atonement (Leviticus 25:9). This symbolism reappears in the apocalyptic eschatology of Matthew 24:31; 1 Corinthians 15:52; 1 Thessalonians 4:16, standing there, as here, for any great event that heralds the fulfilment of a Divine purpose. That purpose, in this instance, is the proclamation of the Year of Redemption: the restoration of the dispersed of Israel from the countries of their exile, of which (Isaiah 19:23) Assyria and Egypt are the two chief representatives. (Compare to Zephaniah 3:10.)