Besides the specific passages from God’s Word, a number of earlier writers expressed this belief. One is Ephraem of Nisbis (306-373), well known in Syrian church history. He stated, “All the saints and elect of God are gathered together before the tribulation, which is to come, and are taken to the Lord…” That sermon was popularly circulated in several languages.
This is not true. The origin of this is a website claiming to have discovered a sermon by Ephraem hitherto untranslated into English entitled, "On the Last Times, the Antichrist, and the End of the World". The author, Grant Jeffrey, cited on this website claims 1. that the author was Ephraem the Syrian and 2. that Paul J. Alexander, author of The Byzantine Apocalyptic Tradition (a copy of which I own), says he believes the sermon to have been authored by Ephraem the Syrian. Neither is true. The author is Pseudo-Ephraem (but the work is also attributed, in one of the four manuscript copies to St. Isidore), a medieval writer or several writers sometime in the 6th to late 7th century who (like many others) attributed his (their) own work to the famous St. Ephraem of the 4th century. Alexander does not conclude that this sermon was by the original Ephraem. Grant Jeffrey misrepresents Alexander.
Alexander's take on this Pseudo-Ephraem passage was that it was a novel way of shortening the days to spare the elect:Pseudo-Ephraem does not refer to the shortening of time. This author, however, mentions another measure taken by God in order to alleviate the period of tribulation for his saints and for the Elect:The import of this is that it was something hitherto unknown as a doctrine, and also that it was something that was not commonplace later.
For all the saints and Elect of God are gathered, prior to the tribulation that is to come, and are taken to the Lord lest they see the confusion that is to overwhelm the world because of our sins.
It is probably no accident that Pseudo-Ephraem does not mention the shortening of the time intervals for the Antichrist's persecution, for if prior to it the Elect are "taken to the Lord," i.e., participate at least in some measure of beatitude, there is no need for further mitigating actions on their behalf. The Gathering of the Elect according to Pseudo-Ephraem is an alternative to the shortening of the time intervals. (p. 210, The Byzantine Apocalyptic Tradition)
I began other research into the teachings of Ephraem on this subject. Ephraem's preferred method of doctrinal instruction was the hymn. He was a prolific author and poet of his time. In his hymns, one can find the virgin birth, the fall of man, the resurrection of Christ, and a host of other Christian doctrines. About the pretribulation rapture (or any other), there is nothing. In a book attributed to Ephraem, though the earliest copy is from the 6th Century, The book of the Cave of treasures a history of the patriarchs and the kings, their successors, from the creation to the crucifixion of Christ. (Tr. from the Syriac text of the British museum ms. Add. 25875, by Sir E. A. Wallis Budge), there is an addendum called "Of the Coming of Anti-Christ". It contains similarities to the piece authored by Pseudo-Ephraem above but makes no mention of a pre-tribulation (or any other) rapture. In fact, the last paragraph indicates (like standard church teaching before) that the believers will have gone through this period[The anti-Christ] becomes a man incarnate by a married woman of the tribe of Dan. When this son of destruction becomes a man, he will be made a dwelling place for devils, and all Satanic workings will be perfected in him. There will be gathered together with him all the devils and all the hosts of the Indians; and before all the Indians and before all men will the mad Jewish nation believe in him, saying, "This is the Christ, the expectation of the world." The time of the error of the Anti-christ will last two years and a half, but others say three years and six months. And when everyone is standing in despair, then will Elijah (Elias) come from paradise, and convict the deceiver, and turn the heart of the fathers to the children and the heart of the children to the fathers; and he will encourage and strengthen the hearts of the believers. (p.270)
I found cited in Alexander's The Byzantine Apocalyptic Tradition Ephraem's (not Pseudo-Ephraem's) commentary on the scriptures which I was able to obtain through inter-library loan. I looked at all the relevant passages said by pre-trib rapturists to teach this doctrine (such as the passage in I Thess). There was no such teaching by Ephraem on the matter.
The bottom line is that
1. Ephraem the Syrian did not write the sermon you mentioned,
2. Ephraem didn't mention anything like this in his hymns or in his commentary on the New Testament,
3. the doctrine was not known in the Christian church before then (remember Alexander's pointing out Pseudo-Ephraim's unique approach),
4. this single sentence did not go on to form the basis of any doctrine in the church in the 6th or 7th century when it first appeared (or appeared in its final form),
5. the concept of this sentence has no counterpart in any Biblical writing.These are only a few gleanings from the rich scriptural evidence used by the Byzantine apocalypses to support their predictions concerning the Antichrist. However, just as in the case of the Last Roman emperor, there are many data of the Byzantine apocalypses on the Antichrist for which there is no or little biblical foundation. Indeed, it is the principal thesis of Bousset's book on the Antichrist that Church fathers and apocalyptic writers rely largely on an extra-canonical tradition about the Antichrist that sometimes supplements, and in other cases conflicts with, canonical Scripture. So far as Byzantine apocalypses are concerned, there are many features for which no biblical evidence could be quoted.This is true, for example, of the data on the Antichrist's hypocrisy, on his relations to the Jews, on the sign of the snake imposed upon his partisans, on his ability to assume different shapes, on the gathering of the saints to God during his rule, and on the association of the Son of Thunder with Enoch and Elijah in their conflict with the Antichrist. (p. 224, The Byzantine Apocalyptic Tradition)
So, if we are in or after the millennium, why are church members still teaching one another?