No, the matter of where Darby received the idea of the pre-trib rapture has not yet been addressed as part of this thread. In fact we have veered off course as we usually do from the original intent of the OP. (This is partly my fault, admittedly!) Though I did enjoy discussing the meaning of the 70th week of Daniel.
Getting back to the intent of the OP. Does it not seem a bit odd that this girl has a vision of a pre-trib rapture and then shortly within the same frame of history, Darby himself writes and preaches about a pre-trib rapture. Now to say that Darby would never have incorporated any theological ideas from Irving's congregation because of his dislike of their core beliefs and practices, is actually not a slam dunk argument. Remember that the Anabaptist were terribly persecuted by the calvinist yet many baptist have strong calvinist beliefs incorporated into as part of their theology. People often incorporate the ideas of the things they agree with even while not particularly liking those whom were the originator of those ideas.
No, the question still remains, where did Darby derive his pre-trib rapture doctrine? Based on my understanding, Darby stated that the idea of the pre-trib rapture came to him as a matter of personal revelation and not as a matter of uncovering a previously understood truth by the process of scouring the early church historical documents.
I must begin by repeating the observation that there is exactly zero evidence that Darby even knew about the alleged vision. Until some such evidence is discovered, any and all allegations about a link are 100% pure, unadulterated, supposition.
But the thing about this that is most remarkable about this supposition is that both Frere and Cuninghame published pre-trib documents in the 1800's significantly before the alleged date of Margaret MacDonald's alleged vision, but no one is interested in claiming that Darby got the idea from them. Nor do they attribute it to Joseph Mede, who in the 1600's wrote about it and even used the word "rapture" in describing it. But they want to ascribe it to Margaret MacDonald because of the perception that her vision was inspired by a demon!
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In post 11, I made the comment that "This false accusation was first made in 1864 by a man named Samuel Prideaux Tergelles. Darby's associates never knew about the accusation until after both Darby and Tergelles had died. But Darby's associate of many years wrote a hotly worded rebuttal of the accusation on the 1880's." But to enlarge on that a little, The rebuttal contained, among other things, the information that Darby had told one of his associates that he had originally gotten the idea from a Mr. Tweedy. (This Mr Tweedy was highly regarded among the Plymouth Brethren, but not nearly as much so as Darby himself. He finished his life as a missionary in Bagdad.) This comment is particularly significant in view of the fact that it was not made in regard to any contention about the source.
The Plymouth Brethren, of whom Darby was one of the main leaders, did not consider the history of an idea as something even significant. Who had believed an idea in the past had, in their minds, zero significance. The only thing that counted was whether of not the scriptures taught it.
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The argument that Darby would not have given the vision any credence whatsoever, even if he had known about it, is far more that the Plymouth brethren's rejection of the core beliefs of Margaret MacDonald's church. It is rather that basing his belief, even in the smallest part, on such a vision would have done violence to Darby's own core beliefs. And he was so rigorous in applying these core beliefs in his own personal life that he caused himself a great deal of hardship, even to the point of splitting the very group he had himself founded, something he did more than once. He could easily have avoided two such splits with only small compromises, but he would not compromise.
Darby himself insisted that the only source for truth was the Bible itself. He wrote, “There can be no new truth, which would not be found in the word.” Also saying “The Scriptures are the only rule or standard of faith and practice.” (From “The Collected Writings of J. N. Darby” second ed., William Kelly, ed., London, G. Morrish, not dated. The first quotation is from Vol 1, pg 350. The second is from Vol 3, pg 98.) These are not just exceptional statements of this very prolific writer, but basic principles that he consistently applied.
An example of this is the following note he wrote to a woman about some dreams she and some of her friends had reported.
“Very dear sister, – I hear that some of the sisters have had dreams about the coming of Jesus. This has given me uneasiness, for although absent in body, I am with you in spirit, desiring and seeking the good of all of you, the dear redeemed ones of our precious Saviour. It is by the word of God, our rule and our light in these last days, that we must abide. I do not pretend to say that God may not give warning by a dream, for the word of God says that He can do so; but we must be much upon our guard. We have no need of a dream with respect to matters revealed by God... You will generally find that sisters are the ones who have seen these things, and I have not, moreover, noticed that it has brought them, or others, nearer to God... So I beg these sisters to weigh these things well, and not to allow themselves readily to put faith in these dreams, as if they came from God. Let them not allow themselves to be carried away by their imagination, lest they should fall into the snare of the enemy, and lest he should take advantage of this to shake the faith of some.” (From “The Letters of J. N. D.”, Vol. 1, pp. 93-94, second ed., William Kelly, ed., London, G Morrish, 1914)
This letter clearly shows that Darby denounced the idea that these dreams had come from God because we should rely only on the word of God. (by this he plainly meant the Bible) Notice also the scornful nature of his comment that “You will generally find that sisters are the ones who have seen these things.” Lest anyone imagine that this letter refers to Margaret MacDonald, please note that the subject was dreams, not a vision. The dreams, and those who had them, were plural, not singular. And the letter, which infers that Darby had only recently heard about the dreams, was dated March 5th, 1845, fifteen years after Margaret MacDonald’s alleged vision.
In addition to rejecting all supposed truth from extra-Biblical sources, Darby also rejected all teaching or preaching by women. He wrote that “I do not accept a woman’s going out to evangelize. I never saw a woman meddle in teaching and church matters, but she brought mischief upon herself and everyone else. If she sits down with a company before her to teach them, she has got out of her place altogether.” (From “The Collected Writings of J. N. Darby” second ed., Vol 26, pg 383, William Kelly, ed., London, G. Morrish, not dated.) Again, he wrote, “A woman cannot be a principle agent in the work. It is contrary to the ways of God. She may help, GREATLY help, but not be the principle agent.” (From “The Collected Writings of J. N. Darby” second ed., Vol 32, pg 341, William Kelly, ed., London, G. Morrish, not dated.)
Further evidence against the accusation that Darby got this idea from Margaret MacDonald’s supposed vision is Darby’s opinion of her group as a whole. She was a member of a group that called itself the "Catholic Apostolic Church." He called this group the Irvingites because their founder and main teacher was a man named Edward Irving.
Darby wrote of this group that:
“The people called Irvingites have been plainly convicted elsewhere of so much false doctrine, false practice,
and false prophecy, and that by many of the Church of God, as to make it, when known, a question only of preserving God’s children against the deceits and crafts of Satan... they have been often charged with holding the sinful humanity of Christ, and many of their teachers and disciples have, to the writer of this and to other persons avowed it -- that He had the carnal mind, but kept it down or dead. Mr. Irving, bold and fearless in the statement of what he held, declared that his nature bristled with sin like quills upon a porcupine; and that the nature with which the Son of man was clothed poured forth from the center of its inmost will streams as black as hell; and that the Augean stable of this nature was given Him to cleanse; and, what was most material, the spirit which they profess to be the Holy Ghost, though it might not sanction the language, expressly sanctioned the doctrine, the doctrine to which it gave its sanction being, that the law of sin was there all-present.
“Now this was so plainly wicked and evil, and contrary to God’s word and Spirit, that they have, since they have been pressed with it, taken great pains, at least the subtler ones among them, to disclaim and deny this. I say the subtler ones; because it has been not long since avowed by some of their teachers to the writer of this. The way they have gotten over the Spirit’s having sanctioned it is, that they were not answerable for what was said, that is, in utterance by the Spirit, before the ordinances were set up. One of these very ordinances said to the writer of this, that the Spirit might have said it through prejudice to please Me. Irving. I only mention this to shew the unhappy degradation to which men may be reduced by giving way to the leadings of an evil spirit.” (From “The Collected Writings of J. N. Darby” second ed., Vol 15, pp 3-4, William Kelly, ed., London, G. Morrish, not dated.)
But it is not only the group that Darby condemned as Satanic, but their alleged prophetic visions. I boldfaced one comment about this above, But in addition to that comment, he further wrote that “It may not be generally known that the ‘gifts’ among the Irvingites were founded on this doctrine of Christ being a sinner in nature like ourselves. Mr. Irving’s statement was that he had long preached the ‘gifts,’ but there was nothing for the Holy Ghost to testify to; but when he preached this doctrine they came as a witness to it. His teaching moreover on the subject was confirmed by what was received as the prophetic power amongst them.”(From “The Collected Writings of J. N. Darby” second ed., Vol 6, pp 450-451, William Kelly, ed., London, G. Morrish, not dated.)
I will add as a footnote that my knowledge of Darby's writings does not come from summaries made by someone else to prove a point. I devoted literally years to a concentrated study of his writings. As a result of this study I honestly believe I have devoted more study to the doctrines of John Nelson Darby than any other living man. And as a further side note, only on the order of five to ten percent of all Darby's writings are even about eschatology. Most of his writing dealt with ecclesiology, which was the main reason I was interested in his writings.