In 1Thessalonians 4:13 to 5:11, Paul teaches about the second coming of Christ. Christians believe not only that Christ died for our sins, rose from the dead, and ascended into glory, but also that he his coming again in the future to judge the world (See 2Th 1:5-10).
Regarding Christians who have died, Paul does not want people to "grieve as do the rest who have no hope" because "God will bring with him those who have fallen asleep"(1Th 4:13-14).
2. Dead and living saints will ascend together
"We who are alive and remain at his coming shall not precede those who have fallen asleep. First the dead in Christ shall rise, then we who are alive and remain shall be caught up together with them"(1Th 4:15-17).
3. Not a silent or secret coming
"For the Lord himself will descend from heaven with a shout, with the voice of the archangel, and with the trumpet of God in the clouds"(1Th 4:16-17).
4. None can know or guess the time
"The day of the Lord will come like a thief in the night"(1Th 5:2,4).
5. Comes when conditions are normal
"While they are saying, 'Peace and safety'..."(1Th 5:3; 2Pe 3:3-4).
6. We must all keep ourselves prepared
"You brethren, are not in darkness that the day should overtake you as a thief, let us be alert and be sober"(1Th 5:4-6).
7. A day of both wrath and salvation
"Sudden destruction will come upon them"(1Th 5:3).
"God has not destined us for wrath, but salvation"(1Th 5:9).
See 2Th 1:6-10 for proof that these occur on the same day.
8. A doctrine of comfort to Christians.
"Therefore comfort one another with these words" (1Th 4:18; 5:11).
Other notes on a thief in the night