The first 8 verses of Apostle Paul's 1 Thessalonians 5 prophecy are easy to understand IF... one has done their homework in the Old Testament histories and prophecies.
1 Thess 5:1-9
1 But of the times and the seasons, brethren, ye have no need that I write unto you.
2 For yourselves know perfectly that the day of the Lord so cometh as a thief in the night.
3 For when they shall say, "Peace and safety"; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.
What was Apostle Paul's subject in the PREVIOUS CHAPTER 4? It was about the event of Christ's future coming and His gathering His Church. Paul is actually continuing... some prophetic events about that day of Christ's future coming.
Those Paul speaks to had no need for him to go over those "times and the seasons" with them, because they ALREADY knew them. So what's that about? Paul is using that "times and the season" about the SIGNS OF THE END OF THIS WORLD. Did you not know that many of those events for the 'end' of this world were first written back in the Old Testament prophets? Don't be lazy, study the Old Testament too. That's all the Thessalonians had available in their day, just the Old Testament Scripture.
OK. So what events in the above was Paul speaking of that will take place at the 'end'? That "day of the Lord" coming "as a thief in the night" idea is one of those Old Testament prophecies about the last day of this world in our future. Even Lord Jesus said He will come "as a thief" (Rev.16:15). Paul then shows from the OT prophets about that "sudden destruction" coming upon those deceived who will be saying that "Peace and safety" at the end of this world. That day of Christ's future coming will... take those by surprise, "as a thief" breaking in at night.
Now the Pre-trib Rapture Theory school will NOT cover those above events about the 'last day' of this world wen Jesus comes to cause that "sudden destruction" upon the wicked. They instead just pull the 1 Thessalonians 5:9 verse out of this chapter and attach it to their false pre-rapture theory. Why? Because these first eight verses by Paul here point DIRECTLY TO THE LAST DAY WHEN JESUS COMES, and not to their fake coming of Jesus prior... to the "great tribulation".
4 But ye, brethren, are not in darkness, that that day should overtake you as a thief.
Paul says they were not in darkness, that what day should overtake them "as a thief"? That "day of the Lord" that Paul mentioned, the "times and the seasons" which is about the SIGNS of the end of this world. That's what he said would not surprise, or overtake, them, again WHY? Because they ALREADY KNEW THOSE SIGNS FROM GOD'S WORD. They understood Paul about that "sudden destruction" event from OT prophecy. God through His prophet Isaiah even showed that destruction will end this present world "at an instant". Where do you think Paul got the idea in 1 Corinthians 15 about those still alive on earth at that "last trump" being 'changed' at the "twinkling of an eye"? It really is... that simple.
5 Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness.
6 Therefore let us not sleep, as do others; but let us watch and be sober.
7 For they that sleep sleep in the night; and they that be drunken are drunken in the night.
8 But let us, who are of the day, be sober, putting on the breastplate of faith and love; and for an helmet, the hope of salvation.
In that above, Paul compares being 'spiritually' asleep with those who are in spiritual darkness. Those in Christ instead are to be 'watching', and remain spiritually sober, and not spiritually drunken in the night.
So who is spiritually "drunken in the night"? Those who refuse to WATCH the SIGNS Lord Jesus and His Apostles gave us in His Word about the very 'end' of this world leading up to His return. That... is what Paul is actually referring to, the teaching Lord Jesus gave in Matthew 24 and Mark 13 commanding us to WATCH, because if the goodman of the house had known in what WATCH the thief would come, he would not have allowed his house to be broken up. Paul here is actually referring to that Message from our Lord Jesus' Olivet discourse.
9 For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ,
KJV
NOW, that specific "wrath" can be understood, because it is NOT Satan's wrath which Paul is pointing to, but to GOD's WRATH upon the wicked with that "sudden destruction" when THEY will be saying, "Peace and safety"!