What Did Jesus Mean by "the Son of Man"?

The term the Son of Man occurs in Matthew 32 times, in Mark 15 times, in Luke 26 times, and in John 12 times. In the first three Gospels the title is always recorded as having been used by Christ of Himself and never by angel, by man, or by demon. Of the 12 occasions in John, 10 are from the lips of Christ; only twice was the expression used by men, and then only for criticism and unbelief: "We have heard out of the law that the Christ lives forever: and why do you say, The Son of Man must be lifted up? Who is this Son of Man?" Those are the only two occasions in all the Gospels where the term is found upon the lips of any but Christ. It is Christ's own description of Himself, and it is the term that links Him to humanity and shows His intimate and positive relationship to the human race.

For particular illustration I take the story of the temptation, where the Lord is seen standing entirely upon the level of humanity. He was in the wilderness, being tempted as man, as representative of the human race; and that is not my view merely, it was His own statement. In answer to the first temptation He said: "It is written, Man shall not live by bread alone." That is to say, in effect, I am in this wilderness on the human level, as the Son of Man taking the place every other person has to take. I obey the law of God that conditions the life of humanity.

In answer to the second temptation, He said: "It is written, You shall worship the Lord your God, and Him only shall you serve." Thus, He put Himself within the Divine limitation of every other human life and declared that He was living according to the law which every other human must obey if he would come to the fulfillment of his life. In answer to the third of these temptations, He said: "It is said, You shall not tempt the Lord your God.” Thus, He declared that the law which governed Him was exactly the same as that which governed other people. Therefore, the terms that indicate His relationship to men are those that prove His absolute kinship with the human race, His complete identification with human experience.
Campbell Morgan