“Son of Man” was a common expression in the Old Testament for “man” or “mankind”, rendered either ben-enosh [“son of man”] or ben-adam [“son of Adam”]. It was the phrase with which God addressed the prophet Ezekiel over 90 times:
The voice said to me: Son of man, stand up! I wish to speak to you ( Ez 2:1).
Often the phrase had a depreciating quality, highlighting human weakness in comparison to God’s strength; from Psalm 8:
When I see your heavens, the work of your fingers, the moon and stars that you set in place—What is man that you are mindful of him, and a son of man that you care for him? (vss. 4-5).
From the prophet Isaiah:
I, it is I who comfort you. Can you then fear mortals who die, human beings [“sons of men”] who are just grass (51:12).
It is curious then that “Son of Man” was Jesus’ favorite title, occurring about 80 times in the gospels. It even appears in His discourses on the second coming:
…you will see the Son of Man seated at the right hand of the Power and coming with the clouds of heaven (Mark 14:62).
The one instance it occurs outside the gospels is in the Book of Acts and demonstrates that over time it had become commonly identified with Jesus. About to be martyred, St. Stephen peers into heaven:
When they heard this, they were infuriated, and they ground their teeth at him. But he, filled with the holy Spirit, looked up intently to heaven and saw the glory of God and Jesus standing at the right hand of God, and he said, “Behold, I see the heavens opened and the Son of Man standing at the right hand of God” (7:54-56).
Some biblical scholars have suggested that Jesus chose the phrase as a title to draw attention to Daniel’s prophetic vision of four kings:
As the visions during the night continued, I saw coming with the clouds of heaven One like a son of man. When he reached the Ancient of Days and was presented before him, He received dominion, splendor, and kingship; all nations, peoples and tongues will serve him. His dominion is an everlasting dominion that shall not pass away, his kingship, one that shall not be destroyed (7:13-14).
While this is clearly a reference to the Messiah, the four kings in the vision were symbolized as animals and Daniel may have been simply stating that this one was in human form. This incidental reference probably does not explain Jesus’ preference for it.
More likely, Jesus chose the title in order to show that His human nature was as real and as important as His divine nature, which His miracles attested to. It was a balancing act: while He called Himself Son of Man, He always referred to God as “my Father” rather than “our Father”, even affirming that “I and the Father are one”.
Jesus may have been well aware that theological controversies about His divine and human natures would arise and that “Son of Man”, as an affirmation of His human nature, would help the early Church deal with the many heresies that would deny it. This is hinted at by the author of “Christology” in the Catholic Encyclopedia (1917). After discussing the title, “Son of Man” he adds,
The true humanity of Jesus Christ was denied even in the earliest ages of the Church. The Docetist Marcion and the Priscillianists grant to Jesus only an apparent body; the Valentinians, a body brought down from Heaven. The followers of Apollinaris deny either that Jesus had any human soul at all, or that He possessed the higher part of the human soul….
St. Paul viewed the humility of Jesus’ incarnation as a standard for us to follow:
Have among yourselves the same attitude that is also yours in Christ Jesus, Who, though he was in the form of God, did not regard equality with God something to be grasped. Rather, he emptied himself, taking the form of a slave, coming in human likeness; and found human in appearance, he humbled himself, becoming obedient to death, even death on a cross (Phil 2:6-8).