In 1 Corinthians 15 Paul teaches that at the moment of the resurrection for all saints, any believers who are still alive moment will instantly exchange their present body for a new body. The exchange for a new incorruptible form is necessary because we are immediately escorted into Heaven with the Lord. But when the exchange of bodies takes place, what happens to the old body?
While the Bible does not specifically say what happens to the bodies of believers who are alive at the moment of our resurrection, there are only two possibilities: the old body is simply abandoned in the same way that a body is left behind at death, or else the old body is transformed into the new body leaving nothing behind.
We prefer the second option, since Paul says explicitly in 1 Corinthians 15:51 that we will not die but we will be changed. Since death leaves a lifeless body behind, Paul seems to be saying that this will not happen in the case of those alive at the resurrection moment. Instead, Paul says our old body is changed (i.e., transformed) into a new body leaving nothing behind.