Why is Jesus Son of Man?
The use of the title “Son of Man” in the New Testament is explained as follows:
“The early Fathers were of the opinion that the expression was used out of humility and to show Christ’s human nature, and this is very probable considering the early rise of Docetism. This is also the opinion of Cornelius a Lapide. Others, such as Knabenbauer, think that He adopted a title which would not give umbrage to His enemies, and which, as time went on, was capable of being applied so as to cover His Messianic claims – to include everything that had been foretold of the representative man, the second Adam, the suffering servant of Jehovah, the Messianic king.”
– Son of Man
The Catechism of the Catholic Church:
53 The divine plan of Revelation is realized simultaneously “by deeds and words which are intrinsically bound up with each other” and shed light on each another. It involves a specific divine pedagogy: God communicates himself to man gradually. He prepares him to welcome by stages the supernatural Revelation that is to culminate in the person and mission of the incarnate Word, Jesus Christ.
St. Irenaeus of Lyons repeatedly speaks of this divine pedagogy using the image of God and man becoming accustomed to one another: The Word of God dwelt in man and became the Son of man in order to accustom man to perceive God and to accustom God to dwell in man, according to the Father’s pleasure.
460: The Word became flesh to make us “partakers of the divine nature”: “For this is why the Word became man, and the Son of God became the Son of man: so that man, by entering into communion with the Word and thus receiving divine sonship, might become a son of God.” “For the Son of God became man so that we might become God…”
St. Thomas Aquinas:
"(2) Our hope is raised up. It is certain that the Son of Man did not come to us, assuming our flesh, for any trivial cause, but for our exceeding great advantage. For He made as it were a trade with us, assuming a living body and deigning to be born of the Virgin, in order that to us might be vouchsafed part of His divinity. And thus He became man that He might make man divine.
(3) Our charity is enkindled. There is no proof of divine charity so clear as that God, the Creator of all things, is made a creature; that Our Lord is become our brother, and that the Son of God is made the Son of man: “For God so loved the world as to give His only-begotten Son.” Therefore, upon consideration of this our love for God ought to be re-ignited and burst into flame."
A reading from the letters of Pope St Leo the Great (Letter 28, 3-4)
“For it must always be said that the one and the same Jesus is truly Son of God, and truly son of man. He is God insofar as in the beginning he was the Word, and the Word was with God, and the Word was God. And he is man insofar as the Word became flesh and dwelt among us.”
Article: Son of Man in the Old Testament: