If the only Scripture to indicate that the last trumpet mentioned in 1 Cor. 15:51,52 were the 7the trumpet, then, of course, we’d have to reject the notion as mere speculation that should be avoided. That is not the case.
First Paul tells us in 2 Tim. 4:1
I charge thee therefore before God, and the Lord Jesus Christ, who shall judge the quick and the dead at his appearing and his kingdom.
and Rev. 22:12
And, behold, I come quickly; and my reward is with me, to give every man according as his work shall be.
Both of these verses indicate that Jesus rewards the righteous and judges the wicked at His coming. If this indeed happens simultaneous with His coming as the Word indicates,then the timing of when He rewards is also an indicator of His coming. Also the “and His kingdom,” shows significance as to the timing is simultaneous with Jesus ruling and reigning forevermore.
There are several events that take place at the 7th trumpet:
1) Jesus rules and reigns forevermore…
And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever.
2) Jesus judges the dead and rewards the righteous…
And the nations were angry, and thy wrath is come, and the time of the dead, that they should be judged, and that thou shouldest give reward unto thy servants the prophets, and to the saints, and them that fear thy name, small and great; and shouldest destroy them which destroy the earth
3) The mystery of God is finished…
But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets
Paul declares a mystery that the rapture happens at the last trumpet.
1 Cor. 15:52
In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed.
So that is a half a dozen verses that all point to the same timing of the 7th trumpet, but that is not the end there is more…
For more see my entry entitled, “the last trumpet rapture.”