In the introduction, we saw that the Thessalonian believers were concerned about their Christian brothers and sisters who had died. Would they, by dying before the return of Jesus, be disqualified from the benefits and glories of that Day of the Lord? Paul writes to dispel their fears and the "ignorance" (v. 13) that has caused this concern (vv. 13-18).
On the basis of the historical fact of Jesus' resurrection, Paul says we have cause to believe that all who put their trust in Him will be resurrected too. Those who have died "in Him" will rise with Him and "God will bring with Jesus" all of these resurrected ones on that Day (vv. 13,14). Those who are physically alive on that Day will also participate, but only after the "dead in Christ" have risen first. That Day will be announced with a heavenly command and all who believe in Christ (both "deceased" and "alive") will "be caught up together... in the clouds to meet the Lord in the air" (vv. 15-17). From that point, the Church will forever be "with the Lord."
This marvelous truth should bring "hope" (v. 13) and "comfort" (v. 18) to all who have loved ones dead in Christ, says Paul. For they're not really dead at all. No, this is not denial of death; this is triumph over death. Our Saviour has risen — and so will we. And He will make sure that when He returns we are all there for the celebration.