There is no doubt about the context in which this appears. A great trumpet is going to be blown, undoubtedly the seventh trumpet. What will happen at the seventh trumpet? The context says that God is going to bring the children of Israel back into their land, showing God making a judgment that involves, not only the people of Israel, but also the land of Israel.
The word that is translated "thresh" is not the ordinary word for that activity. Ordinarily whenever threshing is done, the Bible shows the grain either laid on a firm surface and then beaten with a stick, or taken in hand and beaten against something solid, like a wall. The purpose for this is to break the wheat berries from the stock, and it generally takes a fair amount of force to do this.
The word "thresh" here does not indicate that kind of threshing but a method that is more careful and gentle. This word is applied when a person gently strikes an individual piece of fruit—like an apple, peach, or pear—from the branch, or when the tree is gently shaken so that the fruit falls out.
Here is God's judgment. At that time, the children of Israel will not be in a condition in which they will need to be beaten. Taking all of the scriptures on this together, we find that they will be returning to their land weeping, their wild spirit broken. It has been broken, of course, through the tribulation and the Day of the Lord. So as He is gathering, He is doing it one by one, leading them, as it were, by the hand.
At that time it is God's judgment that the children of Israel will need more than the usual amount of concern. He is indicating not just a separation from the nations, but that an act of purification is also taking place.
John W. Ritenbaugh
Fall Feast Lessons
The context is "[the] children of Israel" being "gathered one by one" (verse 12). "They . . . who are about to perish" seems to refer to the peoples of Israel enduring the time of Jacob's Trouble. The turning point, then, and the beginning of deliverance, is when "the great trumpet will be blown." The Olivet Prophecy correlates to this, for Jesus Christ says,
Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. And He will send His angels with a great sound of a trumpet, and they will gather together His elect [chosen people] from the four winds, from one end of heaven [the Greek word is plural— "heavens"—referring to things within earth's atmosphere (e.g., "the four winds") rather than to the heaven of God's throne] to the other. (Matthew 24:30-31)
The trumpet is a symbol of considerable consequence in the Old and New Testaments. In general, it can signify an alarm of war, a call to assemble, or a command to march (see Numbers 10:1-10). The fourth annual holy day is the Feast of Trumpets, a "memorial of blowing of trumpets, a holy convocation" (Leviticus 23:24; Numbers 29:1). Psalm 81:3-5 indicates Joseph was released from prison in Egypt on the Feast of Trumpets, making for rich symbolism regarding the future release of Israelite captives. God, through the prophets, often uses "Joseph" to represent, not just Ephraim and Manasseh, but also all of Israel (see Ezekiel 37:16-19; Amos 5:6, 15; 6:6; Obadiah 1:18; Zechariah 10:6). In addition, God caused the walls of Jericho to fall after seven successive days of trumpets sounding (Joshua 6:4-20).
Various end-time prophecies show that a trumpet precedes the Day of the Lord (Joel 2:1; Zechariah 9:14-16), when Jesus Christ returns as King of kings and overthrows the nations of this world, establishing the Kingdom of God on earth. The resurrection from the dead is also connected to a mighty trumpet blast (I Corinthians 15:52; I Thessalonians 4:16). While the book of Revelation tells of seven trumpets (Revelation 8:2—11:15), when the last one sounds, "the kingdoms of this world have become the kingdoms of our Lord and of His Christ, and He shall reign forever and ever!" (Revelation 11:15), indicating He has returned. This all shows that the timing of the Second Exodus in general corresponds to the return of Christ.
David C. Grabbe
The Second Exodus (Part Two)
Other Forerunner Commentary entries containing Isaiah 27:13: