The Son of Man was Jesus’ favorite title for himself. You find him using it 29 times in the gospel of Matthew. And that includes his response to the high priest at his trial before the Sanhedrin (Matt. 26:64).
That response makes it clear just what Jesus meant by his use of the term. It was a direct reference to Daniel 7:13-14, and the one like a son of man who came in the clouds of heaven. He approached the throne of God and was given eternal dominion and an everlasting kingdom.
In my vision at night I looked, and there before me was one like a son of man, coming with the clouds of heaven. He approached the Ancient of Days and was led into his presence. He was given authority, glory and sovereign power; all nations and peoples of every language worshiped him. His dominion is an everlasting dominion that will not pass away, and his kingdom is one that will never be destroyed.Daniel 7:13-14 NIV
Jesus was claiming to be this person. And that explains the response of the high priest who tore his clothes and accused Jesus of blasphemy.
The mystery of the incarnation is great. God, the Son, became a man. He did not just wrap himself in flesh. But, somehow, he actually became fully human while at the same time remaining fully God. Son of man refers to Jesus in his humanity. And it is in his humanity that Daniel saw Jesus, one like a son of man, come before the Ancient of Days to be given an eternal dominion and kingdom.
Jesus became the first of a new humanity. And all who put their faith in him will one day join him in that new humanity (1 Jn. 3:2) and have a place in his eternal kingdom that will never be destroyed. There is so much about this that I do not understand. But I am so very thankful that he has called me into his kingdom. And I look forward to what he is even now preparing me for.