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There is not the slightest indication that the event in Luke 17:36 is secret. In this verse, Jesus was describing Noah‘s flood and the destruction of Sodom (Luke 17:26-37). He told how God spared Noah and Lot and destroyed the wicked. And he says specifically that the flood and fire “destroyed them all” (Verses 27, 29).
In each case, a few were taken to safety and the rest were destroyed. Then He added, “Even thus shall it be in the day when the Son of man is revealed” (Verse 30).
To illustrate, Jesus continued, “Two men shall be in the field; the one shall be taken, and the other left” (Verse 36). There is nothing secret about it because all people will see the Lord’s coming “Every eye shall see Him” (Revelation 1:7).
At the second coming, Christ publicly and openly takes the righteous up into the clouds “For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord” (1 Thessalonians 4:16, 17).
Then, the Lord will slay the wicked “And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming” (2 Thessalonians 2:8 also Isaiah 11:4).
That’s why Luke 17:37 speaks of the bodies of the wicked and mentions the eagles gathered around them “And they answered and said unto him, Where, Lord? And he said unto them, Wheresoever the body is, thither will the eagles be gathered together.”
The wicked who are left behind at Christ’s coming are left dead “And I saw an angel standing in the sun; and he cried with a loud voice, saying to all the fowls that fly in the midst of heaven, Come and gather yourselves together unto the supper of the great God; That ye may eat the flesh of kings, and the flesh of captains, and the flesh of mighty men, and the flesh of horses, and of them that sit on them, and the flesh of all men, both free and bond, both small and great” (Revelation 19:17, 18 also Jeremiah 25:33).
In His service,