29  Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. 30  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. 31  And He will send His angels with a great sound of a trumpet, and they will gather together His elect from the four winds, from one end of heaven to the other.

Paul confirms the above, namely, that the man of sin (the antichrist), who is permitted to author the great tribulation, must first be revealed before the coming of Christ and our being gathered unto Him.

1  Now, brethren, concerning the coming of our Lord Jesus Christ and our gathering together to Him, we ask you, 2  not to be soon shaken in mind or troubled, either by spirit or by word or by letter, as if from us, as though the day of Christ had come. 3  Let no one deceive you by any means; for that Day will not come unless the falling away comes first, and the man of sin is revealed, the son of perdition, 4  who opposes and exalts himself above all that is called God or that is worshiped, so that he sits as God in the temple of God, showing himself that he is God. (2 Thessalonians 2:1-4).
John reiterates what Christ had said earlier, that is, that this gathering of the elect by angels takes place after the revealing of Christ on the clouds. He says Christ is revealed when the 6th seal is opened; after this, angels are sent to the four corners of the earth, Israelites are sealed; then the 7th seal is opened wherein seven angels are given, each, a trumpet to sound. The events here are guaranteed to be in sequential order because the seals are named by the order in which they are opened.

12  I looked when He opened the sixth seal, and behold, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became like blood. 13  And the stars of heaven fell to the earth, as a fig tree drops its late figs when it is shaken by a mighty wind. 14  Then the sky receded as a scroll when it is rolled up, and every mountain and island was moved out of its place. 15  And the kings of the earth, the great men, the rich men, the commanders, the mighty men, every slave and every free man, hid themselves in the caves and in the rocks of the mountains, 16  and said to the mountains and rocks, "Fall on us and hide us from the face of Him who sits on the throne and from the wrath of the Lamb! (Revelation 6:12-17).

1  After these things I saw four angels standing at the four corners of the earth, holding the four winds of the earth, that the wind should not blow on the earth, on the sea, or on any tree. 2  Then I saw another angel ascending from the east, having the seal of the living God. And he cried with a loud voice to the four angels to whom it was granted to harm the earth and the sea, 3  saying, "Do not harm the earth, the sea, or the trees till we have sealed the servants of our God on their foreheads." 4  And I heard the number of those who were sealed. One hundred and forty-four thousand of all the tribes of the children of Israel were sealed (Revelation 7:1-4).

1  When He opened the seventh seal, there was silence in heaven for about half an hour. 2  And I saw the seven angels who stand before God, and to them were given seven trumpets (Revelation 8:1-2).

PROCEDURES FOR THE GATHERING
There is a given procedure, in scripture, of how the gathering must be conducted:

1. It will be done by angels
2. It will done using trumpets
3. It will be implemented from the four ends of the earth
4. Israel must be gathered first on earth and receive a seal on the forehead
5. The rapture is the part of the gathering that occurs at the last trumpet
6. The weeds are gathered before the wheat
7. During the gathering, each trumpet signals a particular event

These are explained below.
1-3 are clearly shown in the above mentioned scriptures.
4.ISRAEL MUST BE GATHERED FIRST ON EARTH AND RECEIVE A SEAL ON THE FOREHEAD:
When Christ is revealed and angels are dispatched, the first action is to gather together Israel and put a seal on them. The statement, "Do not harm the earth, the sea, or the trees till we have sealed the servants of our God on their foreheads." Implies that the purpose of the seal is to protect the sealed from the harm, to be occasioned on the earth shortly thereafter when the first 6 angels sound their trumpets. Since the revealing of the son of man on the clouds takes place after the great tribulation (Matthew 24:29-31; Mark 13:24-27; 2 Thes. 2:1-4), those who are sealed here are definitely those who will have been kept in a place of safety and nourishment in the mountainous wilderness throughout the three and a half years of great tribulation (Matthew 24:15-16 - Revelation 12: 6, 14).
When Christ is revealed, remember that before their flight, they are worshipping God in Jerusalem in a manner of the Old Testament (by daily sacrifices, see Daniel 9:27) implying they had not yet believed in Jesus as their promised messiah, given that Christ's sacrifice on the cross is the end of daily sacrifices for those who believe (Hebrews 7:26-27, 10:18). This therefore implies that they do not have the seal of God at this point because whoever believes in Christ will already be having the seal of God (Ephesians 1:13). Also remember that at Christ's coming, the gospel will have already been preached to all nations (especially gentiles, see Matthew 24:14), and thus when He comes, the times of the gentiles will have been fulfilled implying that it will be the time for salvation of all Israel. Therefore their being sealed by angels is the fulfilment of this conditional prophecy.

25  For I do not desire, brethren, that you should be ignorant of this mystery, lest you should be wise in your own opinion, that blindness in part has happened to Israel until the fullness of the Gentiles has come in. 26  And so all Israel will be saved, as it is written: "The Deliverer will come out of Zion, And He will turn away ungodliness from Jacob; 27  For this is My covenant with them, When I take away their sins."

Remember the times of the gentiles are fulfilled when the great tribulation is over.

24  And Jerusalem will be trampled by Gentiles until the times of the Gentiles are fulfilled.

2  But leave out the court which is outside the temple, and do not measure it, for it has been given to the Gentiles. And they will tread the holy city underfoot for forty-two months.

51  Listen, I tell you a mystery: We will not all sleep, but we will all be changed- 52  in a flash, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, the dead will be raised imperishable, and we will be changed.

5  And the angel which I saw stand upon the sea and upon the earth lifted up his hand to heaven, 6  And sware by him that liveth for ever and ever, who created heaven, and the things that therein are, and the earth, and the things that therein are, and the sea, and the things which are therein, that there should be time no longer: 7  But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets.

16  For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first. 17  Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord.
For the avoidance of doubt:

1. Paul says the rapture is a mystery whose occurrence is pegged on the sounding of the last trumpet;
2. John says the mystery of God is fulfilled when the 7th angel begins to sound the 7th trumpet (the last of the 7 trumpets presented in Rev. 8).
3. There is no other mystery in the Bible whose fulfilment is pegged to the sounding of a trumpet apart from rapture
4. Therefore, based on scripture search, comparison and elimination, Paul and John are speaking of the same thing.

Moreover it is further confirmed that the 7th angel's trumpet is what provokes the rapture in the following words.

15  Then the seventh angel sounded: And there were loud voices in heaven... 16  And the twenty-four elders who sat before God on their thrones fell on their faces and worshiped God, 17  saying: ... 18  The nations were angry, and Your wrath has come, And the time of the dead, that they should be judged, And that You should reward Your servants the prophets and the saints, And those who fear Your name, small and great...

We know that the righteous will be rewarded at the rapture, which is also known as the resurrection of the righteous (Luke 14:14). By announcing the coming of the time of the dead, that they should be judged, And that You should reward Your servants the prophets and the saints, after the sounding of the seventh trumpet, the scripture confirms that it is indeed the trumpet of rapture spoken of by Paul, as seen earlier.

24  He put another parable before them, saying, "The kingdom of heaven may be compared to a man who sowed good seed in his field, 25  but while his men were sleeping, his enemy came and sowed weeds among the wheat and went away. 26  So when the plants came up and bore grain, then the weeds appeared also. 27  And the servants of the master of the house came and said to him, 'Master, did you not sow good seed in your field? How then does it have weeds?' 28  He said to them, 'An enemy has done this." So the servants said to him, 'Then do you want us to go and gather them?' 29  But he said, 'No, lest in gathering the weeds you root up the wheat along with them. 30  Let both grow together until the harvest, and at harvest time I will tell the reapers, "Gather the weeds first and bind them in bundles to be burned, but gather the wheat into my barn."
The interpretation of the parable is given hereunder:

37  He answered, "The one who sows the good seed is the Son of Man. 38  The field is the world, and the good seed is the sons of the kingdom. The weeds are the sons of the evil one, 39  and the enemy who sowed them is the devil. The harvest is the end of the age, and the reapers are angels. 40  Just as the weeds are gathered and burned with fire, so will it be at the end of the age. 41  The Son of Man will send his angels, and they will gather out of his kingdom all causes of sin and all law-breakers, 42  and throw them into the fiery furnace. In that place there will be weeping and gnashing of teeth. 43  Then the righteous will shine like the sun in the kingdom of their Father. He who has ears, let him hear.

What delays the end of age is that the wheat and weeds will not have reached full maturity. Therefore the end of age reaches under three conditions:

1. Everyone is marked with a seal - either of Christ (Eph. 1:13) or of the antichrist (Rev. 13:16)
2. The gospel has been preached to all nations for the end to come (Matthew 24:14).
3. The full number of gentiles as planned by God has been saved in order to pave the way for the salvation of Israel according to Romans 11:25-27.

At this point, Israel are the only people in the world without a mark, given that, they were not believers in Christ but needed to be protected in the wilderness from being wiped out from the face of the earth by the beast/antichrist (Rev. 12:13-16). This is why Israel has to be marked first such that everyone on the earth can be identified by the angels for their correct category of harvesting - either wheat or weeds. With all people on the earth marked, it means the angels no longer have the problem of differentiating between the sons of the devil and those of God's kingdom - a longstanding problem they had necessitating them to wait until the end of age before carrying out the gathering - lest in gathering the weeds you root up the wheat along with them. 30 Let both grow together until the harvest (verse 29).
We learn from this parable that the pattern of the harvest is to first gather the weeds and burn them, and not to first gather the wheat in a rapture as implied by the pre-tribulation rapture idea.
It should also be noted that the end of age has been wrongly defined in the past as occurring at the great white throne judgment after the millennial (1,000 years) rule of Christ (Revelation 20). This is demonstrated herewith:

1. Matthew 24:14 pegs the end of age on the completion of the preaching of the gospel to all nations.
2. The end of age in the parable of weeds is all about gathering the harvest (the elect or sons of the kingdom) and Jesus says this follows the event of his being revealed on the clouds (Matthew 24:31). In any case, how can one define our being gathered unto Christ (2 Thes. 2:1) to the exclusion of rapture?
3. We know that the resurrection of the righteous and rapture will occur before the millennial kingdom begins, (Rev 20:4-6). By saying, Then the righteous will shine like the sun in the kingdom of their Father (verse 43), the parable of weeds alludes to the resurrection of the righteous, because we know that we shall shine like the sun after our resurrection or rapture, as explained by Paul here:
   41  There is one glory of the sun, and another glory of the moon, and another glory of the stars; for star differs from star in glory. 42  So is it with the resurrection of the dead. What is sown is perishable; what is raised is imperishable. 43  It is sown in dishonor; it is raised in glory. It is sown in weakness; it is raised in power (1 Cor. 15:41-43).
4. We are told that gathering of weeds means: The Son of Man will send his angels, and they will gather out of his kingdom all causes of sin and all law-breakers (verse 41). We know that the millennial kingdom of Christ will be on the present earth. Therefore this is referring to activity before the inception of the millennial kingdom not afterwards when the final judgment of the dead will be conducted at the great white throne. Looking at the Book of revelation, we therefore understand that it is referring to angels preparing the earth for Christ's kingdom before he comes to reign and we see this practically done before the rapture (when the first six angels sound their trumpets - Chapter 8-10) and after the rapture when the bowls of Gods wrath are poured on the earth (Chapters 15:6-18).

1  Then the fifth angel sounded: And I saw a star fallen from heaven to the earth. To him was given the key to the bottomless pit. 2  And he opened the bottomless pit, and smoke arose out of the pit like the smoke of a great furnace. So the sun and the air were darkened because of the smoke of the pit. 3  Then out of the smoke locusts came upon the earth. And to them was given power, as the scorpions of the earth have power. 4  They were commanded not to harm the grass of the earth, or any green thing, or any tree, but only those men who do not have the seal of God on their foreheads. 5  And they were not given authority to kill them, but to torment them for five months. Their torment was like the torment of a scorpion when it strikes a man. 6  In those days men will seek death and will not find it; they will desire to die, and death will flee from them.