Paul also wrote Timothy that many would DEPART from the faith. Jesus said that the love of many would wax cold.
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... when Paul uses that terminology to describe people departing from the faith.
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... when Paul uses that terminology to describe people departing from the faith.
The basic meaning of the word is "a departure / a departing" (or, "a standing away from [from a previous standing]")... It is up to the context to inform of just "WHAT KIND" of DEPARTURE is meant.
And since there is a "definite article ['the']" with this word (which otherwise is NOT required, for this word), it draws our att'n to the REASON for it HERE (and the Greek grammar guys point out several REASONS for the use of a "definite article" and ONE reason is that it is pointing BACK to something ALREADY MENTIONED [and ALREADY-KNOWN UNTO] the recipients...
BOTH epistles refer to the "Rapture" [event] using a VARIETY of different words and phrases, NOT JUST the ONE in 1Th4:17! but something like TEN TIMES!! [not once had Paul "previously mentioned" TO THE THESSALONIANS *anything* re: "departure FROM THE FAITH" or "SOME FAITH ISSUE" but previously IN THIS PASSAGE *HAD* mentioned OURS/OUR DEPARTURE!, in VERSE 1!! (the SUBJECT BEING COVERED!--*when* it takes place IN RELATION TO the presence [/arrival] of the DOTL! earthly time period of JUDGEMENTS])])