In Matthew 24, where Jesus talks about the end of the age and His return, He mentions that the sign of the Son of Man will appear in heaven. 

Mat 24:30  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.

What is the sign of the Son of Man that will appear in heaven?  The phrase, “the sign of the Son of Man” is only mentioned in Matthew.  None of the other gospel accounts mention it.  This makes it harder to understand, nevertheless, the Bible does explain its meaning.  Before taking a look at this in detail, let’s look at the context.  

Context

At the start of the chapter, the disciples asked Jesus about the end of the age.  Jesus, in verses 4-14, gave a summary.  He said there would be false teachers deceiving many, wars and rumours of wars, famines, pestilences, earthquakes, persecution of God’s people, the gospel of the kingdom would be preached in all the world, and then the end will come.  So, the period leading up to the end is filled with awful events.  After this summary, Jesus gave us something to look out for.

Mat 24:15  “Therefore when you see the ‘ABOMINATION OF DESOLATION,’ spoken of by Daniel the prophet, standing in the holy place”  (whoever reads, let him understand),

The appearance of the ‘ABOMINATION OF DESOLATION’ is an important event because it heralds the start of great tribulation. 

Mat 24:16  “then let those who are in Judea flee to the mountains.
Mat 24:17  Let him who is on the housetop not go down to take anything out of his house.
Mat 24:18  And let him who is in the field not go back to get his clothes.
Mat 24:19  But woe to those who are pregnant and to those who are nursing babies in those days!
Mat 24:20  And pray that your flight may not be in winter or on the Sabbath.

God’s people who are in Judea need to flee quickly.

Mat 24:21  For then there will be great tribulation, such as has not been since the beginning of the world until this time, no, nor ever shall be.
Mat 24:22  And unless those days were shortened, no flesh would be saved; but for the elect’s sake those days will be shortened.

The appearance of the ‘ABOMINATION OF DESOLATION’ indicates the start of great tribulation.  The great tribulation is a time of terrible trouble on the earth that lasts about 3½ years.  See “How long does the Great Tribulation last?”.  The next verses, 23-28, warn about false Christs and instruct that the return of the true Jesus Christ will be obvious. 

The sign of the Son of Man

We have now covered the context and come to the verse in question.

Mat 24:29  “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.
Mat 24:30  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.
Mat 24:31  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.

These three verses are a summary of events which are described in more detail in Revelation 6, which describes the seven seals.  The first four seals are the famous four horses, white, fiery red, black, and pale.  These are respectively, religious deception, war, famine, and disease.  The fifth seal is martyrdom of God’s people.  The sixth seal is heavenly signs.  Let’s look at these three verses (Matthew24:29-31) in more detail with the sixth seal in mind.

Mat 24:29  “Immediately after the tribulation of those days …

The “tribulation of those days” are all the events following the appearance of the ‘ABOMINATION OF DESOLATION’ that Jesus just described in the preceding verses, 15-28.  The “tribulation of those days” is also described by the first five seals of Revelation 6.

It’s easier to see how Matthew 24:29-31 and Revelation 6:12-16 describe the same events if you read them in parallel.

Mat 24:29  “Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; …	Rev 6:12  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.
Mat 24:29  … the stars will fall from heaven, and the powers of the heavens will be shaken.	Rev 6:13  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.
Mat 24:30  Then the sign of the Son of Man will appear in heaven, …	Rev 6:14  Then the sky receded as a scroll when it is rolled up, and every mountain and island was moved out of its place.
Mat 24:30  …, and then all the tribes of the earth will mourn, ….	Rev 6:15  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,
Mat 24:30  …, and they will see the Son of Man coming on the clouds of heaven with power and great glory.	Rev 6:16  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! Rev 6:17  For the great day of His wrath has come, and who is able to stand?”

The sign of the Son of Man that appears in heaven, Matthew 24:30, corresponds to the sky receding as a scroll when it is rolled, Revelation 6:14.  Both follow the heavenly signs, and both precede the tribes of the earth mourning.

Interlude: Old Testament prophecies

Here are some Old Testament prophecies which describe some of the events of Matthew 24:29-31 and Revelation 6:12-16.

Hagai prophesied that Jesus is going to shake the heavens and the earth at His second coming.  Notice how similar this is to Matthew 24:19 and Revelation 6:13.

Hag 2:6  “For thus says the LORD of hosts: ‘Once more (it is a little while) I will shake heaven and earth, the sea and dry land;
Hag 2:7  and I will shake all nations, and they shall come to the Desire of All Nations, and I will fill this temple with glory,’ says the LORD of hosts.

Isaiah prophesied that men will hid in caves from God.  Notice how similar this is to Revelation 6:16.

Isa 2:19  They shall go into the holes of the rocks, And into the caves of the earth, From the terror of the LORD And the glory of His majesty, When He arises to shake the earth mightily.
Isa 2:20  In that day a man will cast away his idols of silver And his idols of gold, Which they made, each for himself to worship, To the moles and bats,
Isa 2:21  To go into the clefts of the rocks, And into the crags of the rugged rocks, From the terror of the LORD And the glory of His majesty, When He arises to shake the earth mightily.

Continued: The sign of the Son of Man

What will the sign of the Son of Man, which is the sky receding as a scroll, look like?  Matthew 24:27 and Malachi 4:1-2 provide the answer.

Mat 24:27  For as the lightning [astrape] comes from the east and flashes to the west, so also will the coming of the Son of Man be.

The Greek word translated “lightning” is astrape, which means lightning, bright shining.  The Greek word translated “flashes” is phaino, which means shine.  Many translations have “shines” rather than “flashes”.

Mal 4:1  “For behold, the day is coming, Burning like an oven, And all the proud, yes, all who do wickedly will be stubble. And the day which is coming shall burn them up,” Says the LORD of hosts, “That will leave them neither root nor branch.
Mal 4:2  But to you who fear My name The Sun of Righteousness shall arise With healing in His wings; And you shall go out And grow fat like stall-fed calves.

When Jesus returns, his coming will be like the sun!  What these verses are telling us is that when the heavens recede as scroll, the whole world will see what appears to be another sun, which shines from east to west, as does the sun.  This “new sun” will appear as some new element of our solar system.  This is the sign of the Son of Man.

The return of Jesus Christ does occur in a single day.  Rather, the whole world will see the sign of the Son of Man, the “new sun” shining in the heavens, travelling from east to west just like the sun, for about a year and a half before Jesus Christ finally descends to the earth.  See “When does the sign of the Son of Man appear?”.

Conclusion

What is “the sign of the Son of Man” that appears in heaven?  It is the appearance of a “new sun” shining in the heavens as the sky recedes as a scroll when it is rolled up.