Luke 221:36
Be always on the watch, and pray that you may be able to escape all that is about to happen, and that you may be able to stand before the Son of Man.”
1 Thessalonians 5:9
“For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ,”
That's one of the things the Pre-trib Rapture school wrongly teaches its believers to do, to take a verse or two out of a whole Chapter and apply the meaning one wants.
The Luke 21 Chapter is Jesus describing the events at the end of this world leading up to His return and the gathering of the Church.
Luke 21 example, in context of the Chapter:
Luke 21:31-36
31 Even so ye also, when ye see these things coming to pass, know ye that the kingdom of God is nigh.
32 Verily I say unto you, This generation shall not pass away, till all things be accomplished.
33 Heaven and earth shall pass away: but My words shall not pass away.
34 But take heed to yourselves, lest haply your hearts be overcharged with surfeiting, and drunkenness, and cares of this life, and that day come on you suddenly as a snare:
35 for (so) shall it come upon all them that dwell on the face of all the earth.
36 But watch ye at every season, making supplication, that ye may prevail to escape all these things that shall come to pass, and to stand before the Son of man.
ASV
Jesus is warning His saints to not be caught off guard about that day of His coming when they begin to see those Signs He gave there on the Mount of Olives for His Church. He even said that day would be a "snare" for those not aware. That's His point.
Apostle Paul taught this same point also in 1 Thessalonians 5, when he said he had no need to tell the brethren there of the "times and the seasons", for they already knew them, and that that day was not to take those in Christ by surprise...
1 Thess 5:1-4
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.
4 But ye, brethren, are not in darkness, that that day should overtake you as a thief.
KJV
And then Apostle Paul tells how those in Christ are to be different than the deceived who are asleep...
1 Thess 5:6-9
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.
9 For God hath not appointed us to wrath, but to obtain salvation by our Lord Jesus Christ,
KJV
As we can easily see, Apostle Paul is warning the Church to be spiritually awake, spiritually sober, watching the Signs of the end (which Jesus gave in His Olivet discourse, which is where Paul pulls from). But the deceived, they are spiritually asleep, drunken in the night spiritually, so they won't be watching those Signs Jesus gave in Luke 21. As a matter of fact, many Church system denominations don't even believe Jesus was giving the main Signs of the end of this world and His coming to gather His Church in that Olivet discourse. Instead, they preach that was history in 70 A.D., or that it was given only for the disciples at Christ's 1st coming! Anyone with common sense ought to quickly recognize there is something wrong with their thinking, with their wrongly saying those Signs in Christ's Olivet discourse are already past history! The very LAST SIGN Lord Jesus gave there is about His future coming! Do you really believe that Jesus' 2nd coming has already happened back in 70 A.D.? How stupid and Satanic of a thought is that??