In "Word Focus" Darrell Grim writes:
The Son of man (v. 23). In Daniel 7:1-8 the writer was describing the Assyrians, the Babylonians, and the Medes and Persians. These were the nations that had held power over Israel. They were cruel and savage rulers. But the writer had a vision that a new power would arise that would rule in a gentle and humane manner. Daniel 7:13, 14 states that one like the Son of man came before the Ancient of Days to receive an everlasting kingdom.
From this passage in Daniel, the Jews dreamed of a golden age when they would be masters of the world. They realized that their nation was so small and weak that God would have to send a champion to lead them to this golden age. So, to them, the Son of man stood for a great, undefeatable ruler sent to them by God. Thus, when Jesus said, “The hour is come, that the Son of man should be glorified,” they would feel that their day of supremacy was at hand. They failed to realize that when Jesus spoke of being glorified, He spoke of crucifixion. When the Jews spoke of the Son of man, they spoke of worldly conquest. When Jesus spoke of the Son of man, He spoke of the victory of the cross.
Source: Jesus, Son of God: Adult Teacher's Insights, page 10.