Matthew 24:21
Matthew 24:2121For at that time there will be great tribulation, unmatched from the beginning of the world until now, and never to be seen again.
is one of the central JW proof-texts for the doctrine of a future "great tribulation" — a coming worldwide attack in which the United Nations will destroy all false religion (including all of Christendom) and then turn on Jehovah's Witnesses specifically before Armageddon brings paradise. The 2016 convention's "bunker video" dramatised this sequence. The verse is read as describing an event still future to our day, not as describing the AD 70 destruction of Jerusalem.
Read with the Synoptic parallel in , which decodes Matthew's "abomination of desolation" as "Jerusalem surrounded by armies." The "great tribulation" Jesus describes is the Roman siege and destruction of Jerusalem in AD 66-70 — a unique catastrophe in Jewish history where approximately 1.1 million people perished according to Josephus (Wars of the Jews, Book 6), the temple was destroyed exactly as Jesus predicted, and not one stone was left on another. anchors the timeframe: "this generation will not pass away until all these things take place." Pair with — Jesus uses the identical "this generation" phrase just verses earlier and unambiguously means his contemporaries. Recognising the AD 70 fulfilment does not eliminate future return; it places future return where and actually put it. The Watchtower has imported a future JW-specific persecution into a verse describing first-century events.