Early dispensationalist taught that Matthew 24:40 was a reference to the second coming and not to the rapture. (check Scofield’s notes) The first reference to the rapture is when Paul said “Behold I show you a mystery.”(1 Cor 15:51) The word mystery means that something new is revealed. I don’t know how the interpretation of Matthew 24:40 got reversed by the mainstream teachers somewhere mid 20th century.
Actually, I am under the impression that the letters to Galatians and 1st Thessalonians came before the letters to the Church at Corinth. And you are doubtless aware of 1Thess4:13-18.
The second coming and the resurrection are one event prophesied in the feast of Trumpets (Yom Teruah), the day of Attonement (Yom Kippur), and the feast of Tabernacles (Sukkot), all of which are linked irrevocably in a 15 day sequence, and commonly called “The Fall Feasts.”
Yom Teruah has always been the event for which “no man knows the day or the hour” because it is the only feast that begins when the new moon shows up at sunset, as peoples eyes adjust to the lower level of light allowing the thin sliver of moon that was in the sky all day long to suddenly become visible.
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