Below are the verses that mention the glory of Christ at His coming in the book of Matthew in reverse order. The question is what is the coming of the Lord in Matthew 25:31. Verses in parenthesis offer additional context.
Matthew 25:31 (NAS): But when the Son of Man comes in His glory, and all the angels with Him, then He will sit on His glorious throne. (Matthew 25:34 (NAS): Then the King will say to those on His right, ‘Come, you who are blessed of My Father, inherit the kingdom prepared for you from the foundation of the world.)
Key points: Son of Man comes in glory, with the angels, sitting on His throne, the saints inherit the kingdom
Matthew 24:30 (NAS): “And then the sign of the Son of Man will appear in the sky, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of the sky with power and great glory. (Matthew 24:34 (NAS): Truly I say to you, this generation will not pass away until all these things take place.)
Key points: sign of the Son Man Appears, all tribes of the earth mourn (Revelation 1:7), they would see Him come with power and glory, with angels (v. 31), it would happen within that generation
Matthew 19:28 (NAS): And Jesus said to them, “Truly I say to you, that you who have followed Me, in the regeneration when the Son of Man will sit on His glorious throne, you also shall sit upon twelve thrones, judging the twelve tribes of Israel.
Key points: they would sit on thrones with Him, they would judge Israel
Matthew 16:27–28 (NAS): For the Son of Man is going to come in the glory of His Father with His angels, and will then repay every man according to his deeds.
28 “Truly I say to you, there are some of those who are standing here who will not taste death until they see the Son of Man coming in His kingdom.
Key points: The Son of Man would come with the glory of the Father (see John 17), with angels, to repay everyone according to their deeds (see Rev 22:12), some alive would see Jesus come in His kingdom (with power per Mark 9:1).
Summary: The Son of Man would come with power and the shared glory of Himself and the Father within that generation before some of His disciples would die. At this time the saints would inherit the kingdom, Israel would be judged along with those who had heard the gospel, and the angels would participate in the gathering of the saints into the kingdom. To distinguish one “coming of the Son of Man in glory with the angels” from another makes no sense in Matthew. Not only is Matthew 24-25 an united discourse, but the entire book of Matthew is united on this subject.
This latter point is seen in the first discussion of kingdoms and glory in the book when the Devil tempts Jesus:
Matthew 4:8–9 (NAS): Again, the devil *took Him to a very high mountain and *showed Him all the kingdoms of the world and their glory;
9 and he said to Him, “All these things I will give You, if You fall down and worship me.”
The entire book is about identifying and defining the Messiah (Matthew 1:1-17). the struggle between Jesus and Satan/ Jesus and the Pharisees throughout the account is a depiction of the early saint's questions about the nature of the kingdom. The book ends with the earthy kingdoms mourning (Matthew 24) and the saints receiving the kingdom (Matthew 25). This is preceded by a final demonstration of the hypocrisy of the Pharisees (Matthew 23).