From Clarke’s commentary:
He shall send his angels - Τους αγγελους, his messengers, the apostles, and their successors in the Christian ministry.
With a great sound of a trumpet - Or, a loud-sounding trumpet - the earnest affectionate call of the Gospel of peace, life, and salvation.
Shall gather together his elect - The Gentiles, who were now chosen or elected, in place of the rebellious, obstinate Jews, according to Our Lord's prediction, Matthew 8:11,Matthew 8:12, and Luke 13:28,Luke 13:29. For the children of the kingdom, (the Jews who were born with a legal right to it, but had now finally forfeited that right by their iniquities) should be thrust out. It is worth serious observation, that the Christian religion spread and prevailed mightily after this period: and nothing contributed more to the success of the Gospel than the destruction of Jerusalem happening in the very time and manner, and with the very circumstances, so particularly foretold by our Lord. It was after this period that the kingdom of Christ began, and his reign was established in almost every part of the world.
To St. Matthew's account, St. Luke adds, Luke 21:24, They shall fall by the edge of the sword, and shalt be led away captive into all nations; and Jerusalem shall be trodden down by the Gentiles, till the times of the Gentiles be fulfilled. The number of those who fell by the sword was very great. Eleven Hundred Thousand perished during the siege. Many were slain at other places, and at other times. By the commandment of Florus, the first author of the war, there were slain at Jerusalem 3,600, Josephus. War, b. ii. c. 14. By the inhabitants of Caesarea, above 20,000. At Scythopolis, above 13,000. At Ascalon, 2,500. At Ptolemais, 2,000. At Alexandria, 50,000. At Joppa, when taken by Cestius Gallus, 8,400. In a mountain called Asamon, near Sepporis, above 2,000. At Damascus, 10,000. In a battle with the Romans at Ascalon, 10,000. In an ambuscade near the same place, 8,000. At Japha, 15,000. Of the Samaritans, on Mount Gerizim, 11,600. At Jotapa, 40,000. At Joppa, when taken by Vespasian, 4,200. At Tarichea, 6,500. And after the city was taken, 1,200. At Gamala, 4,000, besides 5,000 who threw themselves down a precipice. Of those who fled with John, of Gischala, 6,000. Of the Gadarenes, 15,000 slain, besides countless multitudes drowned. In the village of Idumea, above 10,000 slain. At Gerasa, 1,000. At Machaerus, 1,700. In the wood of Jardes, 3,000. In the castle of Masada, 960. In Cyrene, by Catullus the governor, 3,000. Besides these, many of every age, sex, and condition, were slain in the war, who are not reckoned; but, of those who are reckoned, the number amounts to upwards of 1,357,660, which would have appeared incredible, if their own historian had not so particularly enumerated them. See Josephus, War, book ii. c. 18, 20; book iii. c. 2, 7, 8, 9; book iv. c. 1, 2, 7, 8, 9; book vii. c. 6, 9, 11; and Bp. Newton, vol. ii. p. 288-290.
Many also were led away captives into all nations. There were taken at Japha, 2,130. At Jotapa, 1,200. At Tarichea, 6,000 chosen young men, who were sent to Nero; others sold to the number of 30,400, besides those who were given to Agrippa. Of the Gadarenes were taken 2,200. In Idumea above 1,000. Many besides these were taken in Jerusalem; so that, as Josephus says, the number of the captives taken in the whole war amounted to 97,000. Those above seventeen years of age were sent to the works in Egypt; but most were distributed through the Roman provinces, to be destroyed in their theatres by the sword, and by the wild beasts; and those under seventeen years of age were sold for slaves. Eleven thousand in one place perished for want. At Caesarea, Titus, like a thorough-paced infernal savage, murdered 2,500 Jews, in honor of his brother's birthday; and a greater number at Berytus in honor of his father's. See Josephus, War, b. vii. c. 3. s. 1. Some he caused to kill each other; some were thrown to the wild beasts; and others burnt alive. And all this was done by a man who was styled, The darling of mankind! Thus were the Jews miserably tormented, and distributed over the Roman provinces; and continue to be distressed and dispersed over all the nations of the world to the present day. Jerusalem also was, according to the prediction of our Lord, to be trodden down by the Gentiles. Accordingly it has never since been in the possession of the Jews. It was first in subjection to the Romans, afterwards to the Saracens, then to the Franks, after to the Mamalukes, and now to the Turks. Thus has the prophecy of Christ been most literally and terribly fulfilled, on a people who are still preserved as continued monuments of the truth of our Lord's prediction, and of the truth of the Christian religion. See more in Bp. Newton's Dissert. vol. ii. p. 291, etc.