Matt 24: 29-30, “Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. 30 Then the
sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory.
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Macabeus, I see that you are reading this passage in Matt 24 with a futurist mindset. I would suggest to you that there is an alternate way to read this passage that fits much better.
In Mark 13 and Luke 21 which are parallels of Matt 24 the disciples ask 2 questions. When will the temple be destroyed and what will be the
sign that it is about to happen. In Matthew you have 3 questions. The third question is "What will be the sign of the end of the age?".
The first 2 questions in Matthew are the same as Mark and Luke but the 2nd question has different wording in Matthew. "The sign of your coming" in Matthew is the same as "the sign that these things will be fulfilled (about the destruction of the temple) in Mark and Luke.
Jesus came in judgment on Jerusalem in A.D. 70. The sign of His coming was the "abomination of desolation" which Luke tells us are the Roman armies surrounding Jerusalem.
This desolation would be "
the sign in heaven" to the Jewish leaders that "
Jesus is ruling and reigning in Heaven" and that even though they had rejected Him, God had set Him up as ruler of the universe.
The third question, only contained in Matthew, is about the "sign of the end of the age". This is why Matthew's Olivet discourse is so much longer than Mark and Luke's. Matthew is addressing the end of the world and Christ's second coming.
Jesus tells us there will be no sign in verse 36. There were plenty of signs leading up to Jerusalem's destruction since Matt 24: 4-34 is about A.D. 70 and before, but verse 36 begins to answer the disciples 3rd question. The end of the world. Jesus says in verse 36 there is no sign. He will come as a thief. Matthew 25 is all about the second coming and the end of the world and that is why you don't see those in Mark or Luke's Olivet discourse because their discourse's are about A.D. 70 and before primarily.
I offer this to you as another way to think about the Scriptures for your consideration.