Make that case with John's epistolary.
I don't form sound belief based on others' opinions.
I don't form sound belief based on speculation, either. We cannot wholly escape that problem because, in this instance, scripture does not explicitly explain itself but any inferences we make should/must be based on what is explicitly stated.
That's hogwash. The reason it is hogwash is because that is not how the original readers would have, nor could have understood John's words. That interpretation violates the precept of original intent and original understanding. The first century Christian would never have thought a mention of locusts' sounds was a reference to 21st century helicopters
(as some believe) or fire from heaven as a reference to space-based lasers
(as some have asserted). We start our (speculative) answer to this op's inquiry with what the original author and his original readers would have understood, not what the text can be made to mean in light of the later institutionalization of Christian religion and scripture. Nothing in that vein is going to be correct.
In preparation for the discussion of this op I re-read John's first epistle. I encourage all the participants to do the same. Leading up to 1 John 2:18, John's stated purpose is, "...
so that you may not sin," and to remind his readers that if they do sin, they have a specific, appropriate response available. Because they know Christ, are themselves strong and have the word at work within them they have, can, and will overcome. This is a theme that runs through all of John's letters and his apocalypse. Before he mentions the last hour's presence, he notes the world (
kosmos) is passing away, but his readers will abide, continue through, or remain through the age (
aiona). That is John's stated set up for his comment about the last hour. Absent his mention of the antichrist and the subsequent coming of Christ, that preface would be sufficient for understanding the reported "
last hour." The planet did not literally pass away. If it had, we would not be here having this conversation. The
kosmos is therefore a reference to one of the other meanings of that word, such as the system of the world, the worldly system. But John does lay out a sequence of events, beginning first with the arrival of the antichrist (which is why I couched my op-reply in that context rather than the end of the world or the coming of Christ. That, the antichrist, was on their mind, not just the subsequent coming of Christ.
John states "
they went out from us." That sounds to me like they were either poseurs or had already been discharged. Because John defines his term "
antichrist" for us we know what they believed and implicitly why they went out from the "
us," the Church. They denied the Father and the Son, and Jesus came from the Father in the flesh. I do not read anything about them coming out and going back in.
So make the case for the original readers of John's first letter understanding the antichrist had infiltrated, or was going to, the Church.