While on earth, Jesus Christ exclusively identified Himself as the Son of Man, instead as the Son of God, as a way to avoid speaking in the first person and in modest reference to Himself (Matt 12:8; Heb 2:5-9).

Introduced by the prophet Daniel, the phrase "Son of Man" is portrayed as the future King who returns in a spectacular manner.

Jesus Christ makes the connection between the Son of Man and the Messiah who atones for iniquity.

Seventy weeks have been decreed for your people and your holy city, to finish the transgression, to make an end of sin, to make atonement for iniquity, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy place. So you are to know and discern that from the issuing of a decree to restore and rebuild Jerusalem until Messiah the Prince there will be seven weeks and sixty-two weeks; it will be built again, with plaza and moat, even in times of distress. (Dan 9:24-25)

just as the Son of Man did not come to be served, but to serve, and to give His life a ransom for many. (Matt 20:28)

Jesus Christ also makes the connection between the Son of Man and the Eschatological Judge.

"But in those days, after that tribulation, the sun will be darkened and the moon will not give its light, and the stars will be falling from heaven, and the powers that are in the heavens will be shaken. Then they will see the Son of Man coming in clouds with great power and glory. And then He will send forth the angels, and will gather together His elect from the four winds, from the farthest end of the earth to the farthest end of heaven." (Mark 13:24-27)

But He kept silent and did not answer. Again the high priest was questioning Him, and saying to Him, "Are You the Christ, the Son of the Blessed One?" And Jesus said, "I am; and you shall see the Son of Man sitting at the right hand of Power, and coming with the clouds of heaven." (Mark 14:61-62)

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. (Matt 16:27)

After His death and resurrection, Jesus Christ is portrayed in glory; the Son of Man and the eschatological return of the glorified King and Judge are One.

Then I looked, and behold, a white cloud, and sitting on the cloud was one like a son of man, having a golden crown on His head and a sharp sickle in His hand. And another angel came out of the temple, crying out with a loud voice to Him who sat on the cloud, "Put in your sickle and reap, for the hour to reap has come, because the harvest of the earth is ripe." Then He who sat on the cloud swung His sickle over the earth, and the earth was reaped. (Rev 14:14-16)