'Behold, I tell you a mystery. We shall not all sleep, but we shall all be changed. In a moment, in the twinkling of an eye, at the last trump. For the trumpet will sound, and the dead will be raised incorruptible, and we will be changed.'
The answer lies in a mystery of God now revealed. And that is that although we shall not all die because some will be living when Christ comes, nevertheless whether living or dying we who are His shall all be changed, shall be transformed. In a moment it will happen, as quick as the eye can blink, for we shall all be changed at the sounding of the last trump. For when that trumpet sounds, the dead will be raised in their new form as incorruptible and undecaying, and the living saints will be transformed.
The ‘we' indicates the possibility, but not the certainty, that Paul will still be alive when Christ comes. It basically means ‘we who are His'. There will be some Christians living when the Lord comes.
Reference to the last trump in this way would naturally be seen as indicating the end of all things physical. The battle is over. The final trumpet is sounded. It seems to be linking back with 1 Corinthians 15:23-26 and saying that at this time God is bringing all things finally to completion. Compare Matthew 24:31; 1 Thessalonians 4:16. It is God's call to final deliverance for the righteous and final judgment for the unrighteous. However, those who believe in a Millennium and a post-rapture tribulation have a difficulty here, for they have to try to fit it into their schemat by some means or other, none convincing. For in context here it is difficult to conceive that Paul could have spoken like this had he not thought that this indicated the final glorious hour, the end of all things physical (compare 1 Corinthians 15:23-26). The whole passage rings with finality. From that time on death is no more. The eternal future begins. He is not obviously speaking of a stage in the process of events, but of the final triumph of God when creation is restored.