To a modern reader, "the Son of Man coming on the clouds" sounds like the Second Coming — a physical, visible, global event. But to a first-century Jewish audience steeped in the Hebrew scriptures, this language had a very specific meaning.
In Daniel 7:13, the Son of Man comes to God on the clouds — he travels toward the Ancient of Days, not toward earth. The "coming" is an ascension and enthronement, not a descent. It describes the moment when the Son of Man receives authority, dominion, and a kingdom.
"In my vision at night I looked, and there before me was one like a son of man, coming with the clouds of heaven. He approached the Ancient of Days and was led into his presence. He was given authority, glory and sovereign power."
Daniel 7:13–14
When Jesus says "they will see the Son of Man coming on the clouds with power and great glory," he is describing his vindication and enthronement — the moment the watching world would know that his claims were true. The destruction of Jerusalem and the Temple was the sign. The covenant God had maintained through that Temple system was being decisively ended, and the kingdom of God — through the risen, ascended, reigning Christ — was being fully established.
The generation he promised did see it. They saw the Temple destroyed exactly as he said. They saw the sign he promised. And many of them lived to tell it.