God prepares us for the overwhelming greatness and glory of Christ's return. He wants you and me to know what is going to happen, that this amazing text, verses 29-31, has not yet been fulfilled in its literal sense, but that it will be. And when it is fulfilled, there will be no question, no debate, no confusion, because Christ will come, the heavens will be shaken, the unrighteous will know that judgment has come upon them, and those of us who are believers will experience rapture or resurrection from the dead. Our Lord is instructing and preparing us for the coming of this event.