Son of Man is a title of humility, meaning that the one who bears it is just like all other people, or perhaps not even worthy of consideration.
In Numbers 23:19 we see the phrase son of man used to imply the need for repentence. In Job 25:6 man is refered to as a maggot, and the son of man a worm. In Psalms 8:4, 80:17, and 144:3 son of man is referred to as one whom God has been merciful and gracious to, with the implication that he is not worthy of it.
When God spoke to Ezekiel He regularly addressed him as son of man. And often the things that God told Ezekiel to do were very humiliating and degrading. This shows that God did not hold Ezekiel in a position of high esteem, but deined to speak to him anyways.
I think it is with this in mind that Jesus referred to himself as Son of Man when speaking about His humiliation, suffering, and death.1 By using this title Jesus was showing himself to be one of the people, rather than in some position of authority over them, which the title Messiah or Christ implies. In other words, He used this title to refer to His humanity.
Daniel gives us an interesting twist to the title Son of Man. In Daniel 7:13 he sees a vision of one “like a Son of Man” coming from heaven. This heavenly figure is distinguished. He is presented to the Ancient of Days and given dominion, glory, and a kingdom. Even though He appears to be a man (like a son of man), He is actually much more than a man.
The implication of Daniel’s vision and the way he words it, I think, is that this heavenly figure comes in lowliness and humility (like a son of man) but is actually God. In other words, He is God in human form. Clearly, Daniel is talking about Jesus.
This point is what made the Pharisees so upset with Jesus. They understood that when Jesus was referring to Himself as the Son of Man, He was not simply referring to Himself in a humble way, but He was alluding to Daniel’s vision, and making Himself equal with God - even claiming to be God Himself. They couldn’t accept that Daniel’s vision was being fulfilled by one so lowly as a peasant from Nazareth. They wanted a Davidic king to conquer their enemies and enrich their nation. To them Jesus was too much like a son of man.
Jesus used the title Son of Man for Himself around 70 times in the New Testament. And it’s worth noting that when other people refer to Jesus in the Bible they usually use the title Christ, but when Jesus refers to Himself He usually uses the title Son of Man. As a title Son of Man does not appear much in the Old Testament - although it does appear quite often as a general phrase. The only other semi-biblical place where this title is used as a title is found in the Book of Enoch, where it appears three times in a special segment known as the Book of the Messiah.2
So why did Jesus use this title more than any other (Son of God, Son of David, Christ, …)? The answer is not immediately apparent. One reason that stands out to me is because those other titles were too specific to Israel, but the title Son of Man applies, and appeals, to all people. And Jesus did not only come to save the Jews, He came to save everyone.
To those who don’t know God, the title Son of God would imply that Jesus is more than human, and out of reach to mere mortals. The title Son of David would imply that Jesus only came to fulfill Jewish prophecy, which would separate Him from the rest of the world. The title Christ implies kingship or priesthood - again making Jesus seem out of reach to poor sinners. But the title Son of Man gets to the heart of Jesus’s true mission - to come and save all people who believe in Him, no matter their nationality or station in life.
The definition of son of man from the online bible says: 3
used by Christ himself, doubtless in order that he might intimate his Messiahship and also that he might designate himself as the head of the human family, the man, the one who both furnished the pattern of the perfect man and acted on behalf of all mankind. Christ seems to have preferred this to the other Messianic titles, because by its lowliness it was least suited to foster the expectation of an earthly Messiah in royal splendour.
Jesus is the Son of Man because He came to save all mankind from sin and death. He created us in His image, and He loves all of us. He came to show us that He knows us, and, since we are His image bearers, He understands us more than we can imagine. Yes, He is the Son of God, the Son of David, and the Christ, but He wants us to know Him, and trust Him, and love Him, so He showed us that He is the Son of Man.
Numbers 23:19 (NASB95) “God is not a man, that He should lie, Nor a son of man, that He should repent; Has He said, and will He not do it?
Job 25:6 (NASB95) How much less man, that maggot, And the son of man, that worm!”
Psalm 8:4 (NASB95) What is man that You take thought of him, And the son of man that You care for him?
Daniel 7:13-14 (NASB95) “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.
Matthew 8:20 (NASB95) Jesus said to him, “The foxes have holes and the birds of the air have nests, but the Son of Man has nowhere to lay His head.”
Matthew 9:6 (NASB95) “But so that you may know that the Son of Man has authority on earth to forgive sins”—then He said to the paralytic, “Get up, pick up your bed and go home.”
Matthew 12:40 (NASB95) for just as JONAH WAS THREE DAYS AND THREE NIGHTS IN THE BELLY OF THE SEA MONSTER, so will the Son of Man be three days and three nights in the heart of the earth.
Matthew 16:27 (NASB95) “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.
Matthew 20:18 (NASB95) “Behold, we are going up to Jerusalem; and the Son of Man will be delivered to the chief priests and scribes, and they will condemn Him to death,
Mark 14:41 (NASB95) And He came the third time, and said to them, “Are you still sleeping and resting? It is enough; the hour has come; behold, the Son of Man is being betrayed into the hands of sinners.
Mark 14:62 (NASB95) 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.”