Any time Mark's gospel refers to Jesus as the "Son of Man", it means that the reader needs to think about the book of Daniel (especially Dan 6 & 7) and think about the implications for what Jesus is doing at that point in the gospel.
The first century readers of the book of Daniel observed that the famous story of Daniel and the Lions' Den and the not-so-famous vision of the Son of Man are effectively the same story. In the first story, Daniel is Israel, the courtiers are the gentile nations, and Darius represents the divine judge who vindicates Daniel, raises him up from his "tomb" and throws the enemies in instead. In the second, the "one like a son of man" is Israel, the beasts out of the sea are his tormenters, and the Ancient of Days is God, who destroys the beasts and ascends the one like a son of man to share His divine throne.
Therein is the shock and scandal of the title "son of man". Jesus is the new "Daniel" and the new "son of man", who is representing the true Israel, and is thrown into the tomb by the "beasts", which ironically are the Pharisees, Sadducees, and scribes. In the end, God raises Jesus from the dead and ascends Him to share the throne of God, while Jerusalem is destroyed in 70 AD.
Hence, all references to the "son of man" in Mark are implicitly a reference to Jesus' suffering and death, sleeping on the sabbath, being raised, and the eventual destruction of Jerusalem.
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