At the Rapture, Jesus will descend from Heaven with a shout (calling for the saints at the resurrection). (1 Thess 4:16) with the voice of the Archangel and the trump of God. I assume the trump of God is the voice of God. It seems to me that if we are changed into our new, glorified bodies at that time, how can all this happen in a twinkling of an eye? I’ve also been taught that all this will be a secret event, the Rapture, but at the Second Coming, every eye shall see him. If the Rapture is secret, won’t the Archangel’s voice and trump of God be loud enough to wake the dead, since at that time the dead will rise first?
The trump of God is actually the sound of a trumpet blowing. We don’t know how God can change us instantaneously, only that the Bible says it will happen in a flash, in the twinkling of an eye (1 Cor. 15:51-52). As for the rapture being a secret event, this means no one knows when it will happen, there won’t be any advance warning to alert us, and it will all be over before anyone realizes what’s happening.
After it happens, it won’t be a secret anymore because millions of people will suddenly be missing. Unbelievers won’t know exactly what happened. However, there will be many who had heard of the rapture but didn’t believe it would really happen, and didn’t prepare them selves to go. In other words they will have not have taken the essential step of accepting the Lord’s death as payment for their sins. They will know exactly what happened and will tell everyone they see. I think this will spark one of the greatest revivals the world has ever seen, and many will die for their new found faith. These are the martyrs described in Rev. 7:9-17.