Death is not the end.
In 1 Thessalonians 4:13-18, Paul taught his readers that Jesus died and rose again, and that Jesus would return to take them home. He also instructed them how to live until Jesus came back again.
However, they had a concern with those who had "fallen asleep" - a common reference to death. They needed to know that those who had died before Jesus returned would be given new life. The Lord will gather to Himself those who are His.
Rather than arguing over how this passage fits into the timeline of the doctrine of end times, let's focus on the joy that will be ours at Christ's return. Let's live ready in light of the fact that His return is imminent - i.e. He could return at any time.
We do know that there is sorrow when we lose loved ones. There is grief and deep pain - that's normal. But when those loved ones had received Jesus for their personal salvation, there is peace and hope. There's no sense of hopelessness when a person knows Jesus.
So then, how do we live ready for Christ's return?
1. Have a relationship with Jesus: Believe that His sacrificial death on the cross is the only way you can be saved from your sin and receive Him as your personal Savior. (Acts 4:12, John 1:12)
2. Grow in your faith. (2 Peter 3:18)
3. Share with others so they can have hope too. While we're still here on this earth, we have a job to do in serving Jesus. (1 Peter 3:15, Galatians 5:13)