If you read 1Thes.4:13-18 and 1Cor.15:50-53 is pretty clear the Bible is talking about a literal and instantaneous transformation of believers from an earthly mortal body into the immortal "resurrection" body. The big debate however is not "if" but "when"
Pre-Tribulation.... Post Tribulation or even Mid-Tribulation which one is it ? To be honest i'm still undecided but good video to get you thinking....