Why do believers need to receive a new body before entering God's presence?
Believers need a new body because this old body is corruptible and mortal, unfit for glory. Paul teaches that not all will sleep, but all will be changed, for this corruptible must put on incorruption and this mortal must put on immortality, making them fit for eternity in God's presence.
Les explains that this change is a secret or mystery that Jesus and the Old Testament never mentioned, but Paul reveals. Enoch was an example of one translated, yet Scripture gives no indication of a group of living people suddenly gone until Paul. The reason is that we cannot go to glory in this old body. Those who die will experience resurrection with a new body; those alive must also be changed, suddenly, in a moment, in the twinkling of an eye, at the last trump. The dead are raised incorruptible, and believers are changed because corruptible must put on incorruption and mortal must put on immortality, making them fit for eternity in God's presence.