My understanding, speaking as a former non-denominational Christian who read a lot of End Times literature, is that there are 3 theories of the Rapture. To understand them, you have to know about the Tribulation.
(BTW, I am explaining these as I have read or heard them, I am not advocating them.)
The Tribulation is the 7 year period that the Antichrist will initiate when he makes a covenant with Israel. Why 7 years?
“And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate. [Dan. 9:27]”
(It takes a real leap in time to get to this “one week” at the end of time, when verse 26 speaks of the cutting off of the Messiah.)
So here are the 3 theories:
PreTrib Rapture: This is what all the “Left Behind” books teach. There will come a day when “true Christians” will disappear “in the twinkling of an eye [1 Cor. 15:52]” The next words of the verse are “at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed.” However that doesn’t stop Hal Lindsay and others from saying this happens before the Tribulation. The belief here is that Christians (“true Christians”) will not go through the Rapture, because for some reason they are saved from it. I can’t remember the verse, but somehow it applies to the last generation of Christians and not obviously to the saints and martyrs of the past 1900+ years. (That’s because so many of the saints and martyrs are Catholic, and Catholics aren’t “true Christians” because they “worship” Mary and the Pope, etc. I don’t think they’ve come out and said that, but I’m putting several ideas together. Like they do.)
MidTrib Rapture: Basically, since Dan. 9:27 above states that since the Antichrist is going to desecrate the Temple after 3 1/2 years (for context, see below), that will be the time of the “falling away.” This is central:
“Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him,
That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.
Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
Remember ye not, that, when I was yet with you, I told you these things?
And now ye know what withholdeth that he might be revealed in his time.
For the mystery of iniquity doth already work: only he who now letteth will let, until he be taken out of the way.
And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:” [2 Thes. 2:1-8])
This desecration of the Temple (the abomination of desolation) is when the Antichrist reveals himself as such. Up until then, he has deceived the world (except the preTrib Rapturists). The midTribbers will be the ones who “taken out of the way,” in other words true Christians would have the Holy Spirit and the Holy Spirit is the one “who now letteth.” A lot of this comes from taking all these verses of the End Times and putting them all together into one context, and then moving the pieces around. I’m not saying this in disrespect to Scripture, I am pointing out that all this “placing into context” is very subjective on the parts of the interpreters. (And also, the Temple in Jerusalem must be rebuilt.)
Finally, there is the PostTrib Rapture. I feel pretty sure that this is the correct interpretation. It is the Second Coming. “For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:” [1 Thes. 4:16]
Oddly, most of the End Times interpreters I have read are fervent preTrib Rapturists. It seems counter-intuitive, and it takes some real bending of context to believe that 7 years PRIOR to the Second Coming of Christ, He will return and lift the “true” Christians up and away from tribulation, and then come again for what would amount to a Third Coming.
First, “dispensationalists” are a subset of Protestants. Second, the “Left Behind” book and movie series is about the rapture, and was written by Protestants.