He said to him, "Most assuredly, I tell you, hereafter you will see heaven opened, and the angels of God ascending and descending on the Son of Man."
Why did Jesus prefer this title?  "Son of God" was a title that carried with it; in the popular mind, the meaning King of Israel, a fact proved by Nathaniel's usage of the two together just a moment before; and it would have been disastrous for the Lord to have allowed the multitudes to crown him "king," a thing many of them were eager to do.  It was clearly for the purpose of preventing such a thing that Jesus so often used the other title, "Son of man," a title which was not generally known and understood by the people and which was thus free of the connotation of an earthly kingship of Israel.  It was absolutely imperative for our Lord to have avoided any semblance of claiming the literal Solomonic throne of Israel; for, if he had been unsuccessful in such avoidance, the Pharisees might have been able to get him crucified for sedition.  It will be remembered that that is exactly what they tried to do anyway; but so completely had Jesus thwarted them, that they finally admitted to Pilate that they desired his condemnation for claiming to be the Son of God (John 19:7).  However, if Jesus had permitted the widespread use of that title earlier, some radical mob would have proclaimed him "King" and thus have provided sufficient grounds for a charge of sedition.