"Son of Man" is a title that Jesus often applied to Himself, though it is rarely used elsewhere in the New Testament or early Christian literature. The title is a reference to the prophecy of Daniel Chapter 7:
"I kept looking in the night visions, And behold, with the clouds of heaven One like a Son of Man was coming, And He came up to the Ancient of Days And was presented before Him. “And to Him was given dominion, Glory and a kingdom, That all the peoples, nations and men of every language Might serve Him. His dominion is an everlasting dominion Which will not pass away; And His kingdom is one Which will not be destroyed," (Daniel 7:13-14).
The description of this figure as "one like a Son of Man," is probably to contrast Him with the beastly figures that represented the pagan kings and kingdoms of the world earlier in the vision. Many Rabbinic Jewish sources identify this figure as the Messiah, Son of David.1 Jewish Apocryphal works from the period even identify the Son of Man as an ancient, heavenly figure hidden before God who descends to deliver the people and is even worthy of worship.2 When Jesus called Himself the "Son of Man," it was no humble appeal to His humanity. It was a declaration of His Messianic authority and even to His divinity. Note the reaction Jesus receives when He applies this prophecy to Himself before the Jewish authorities:
"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.” Tearing his clothes, the high priest said, “What further need do we have of witnesses? You have heard the blasphemy; how does it seem to you?” And they all condemned Him to be deserving of death," (Mark 14:61-64).
They considered this claim to be blasphemy because they understood Jesus divine intention in applying this passage to Himself. They knew He was claiming to be much more than just a human savior. A similar incident occurred at the trial of Steven in the Book of Acts. Note what finally provokes the crowd to kill him:
"But filled with the Holy Spirit, he gazed into heaven and saw the glory of God and Jesus standing at the right hand of God. “Look,” he said, “I see the heavens opened and the Son of Man standing at the right hand of God!” But they covered their ears, and with a loud shout all rushed together against him. Then they dragged him out of the city and began to stone him; and the witnesses laid their coats at the feet of a young man named Saul," (Acts 7:55-58).
Jesus appealed to this idea of a heavenly Son of Man elsewhere. too. For example, when He said to Nicodemus:
"If I told you earthly things and you do not believe, how will you believe if I tell you heavenly things? No one has ascended into heaven, but He who descended from heaven: the Son of Man. As Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up; so that whoever believes will in Him have eternal life," (John 3:14-15)
Jesus thus identifies Himself as the Son of Man who descended from heaven, and further as the one whom must be believed in to receive eternal life.
Daniel 7 specifically says of the Son of Man that, "to Him was given dominion, Glory and a kingdom, That all the peoples, nations and men of every language Might serve Him. His dominion is an everlasting dominion Which will not pass away." The word for "serve" here can also mean worship. The NIV, for example, reads that "all nations and peoples of every language worshiped him." This may well be connected to Revelation 7, where people of every nation, tribe, and tongue sing praises to the Lamb before the throne of God in heaven. It even speaks of "the Lamb in the center of the throne," meaning that Jesus sits on the very throne of God!
At any rate, it is clear that the title of Son of Man is a Messianic title that carried with it divine identity so that for a mere man to claim this title for himself would constitute not only falsehood but blasphemy. Jesus could rightly call Himself the Son of Man because He is indeed both the promised Messiah and God in flesh.