We find the old testament revealed in the new when we read the new in the light of the old.
He said to them, “How foolish you are, and how slow to believe all that the prophets have spoken! 26 Did not the Messiah have to suffer these things and then enter his glory?” 27 And beginning with Moses and all the Prophets, he explained to them what was said in all the Scriptures concerning himself.
...so, you think the entire mystery was the Messiah? Are you aware that the prophets spoke of things concerning the end of world as well? This passage does not say anything about the mystery of God. But this does:
"But in the days of the voice of the seventh angel, when he is about to sound his trumpet, the mystery of God will be fulfilled, just as He proclaimed to His servants, the prophets.”---Revelation 10:7
yes, the entire mystery is the messiah. yes, the prophets spoke of the end of the world as well. the prophets were speaking of the messiah. Nobody else. Jesus Christ is the end of the world, in the philosophical sense of the word "end". The purpose of the world, as it were.
This one is tricky. Lets look at it from a different angle for full understanding.
What is "the Day of the Lord"?
What takes place during this event?