HERETIC ALERT
Isaiah 1:18
Without discussion, how can reality ever be discerned? And without differing opinions, how can there be discussion? It may be possible to share opinions one has heard without sharing those opinions and thereby falling into heresy. One opinion is that everything contradicting God is false but that not contradicting God does not guarantee veracity.
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Disrespectful? Yes. Chamberpot focus? (I was unable to read that but thank the moderator for sparing us.) Moving on, I appreciated this question being raised. Will Baptists be all alone in Heaven? Here a number of factors come into play, relating to
[A] what constitutes a Baptist and
[B] ditto for Christians. The prime example here—since we know He's already in Heaven, having been seen there—is Jesus. Can we say He was a Baptist? As a boy, sure, indoctrination into some other creed took place. Clearly though it was not very adhesive, since as a young man He chose baptism BY A BAPTIST. Let's take a more recent (generic) example: an Episcopalian seeks to follow Christ. In what passes for the Churches they have, generally there is no font. Perhaps a small dish on a plinth but only rarely (if at all) would there be provision for immersion. In those cases, quite often a request to the nearest Baptist Church is made and the baptism occurs there. Will that person be in Heaven?
Assuming there are no idols "back home" and the order of service is not explicitly blasphemous, I can't see why not on the facts provided. On the off chance that an Anglican cathedral exists somewhere with either a proper font for adult baptism or access to a river (or even one of those surf congregations in the South Bay area) (although these are very unlikely to be doctrinally sound) ("unlikely" and "not" however are different things) it could be that full immersion is possible. But if coming up out of the water the first thing one saw was a revolting great big idol of Jesus, not improbable in a cathedral, the baptism would not have been valid and in all likelihood a direct blasphemy against Christ. The Holy Spirit would not descend and if it seemed to, that would be a demon as any manifestation of anything is anywhere there are idols.
Even a Presbyterian could accept Jesus as personal Lord and Friend and get to Heaven, provided the usual obstacles were avoided. Catholics, Mormons, Zoroastrians and so on have no hope. First they'd need to become Christians and follow the teachings of Jesus – in the last case, that's quite possible and whatever the Zoroastrian equivalent of a Pastor is would agree. I'm not sure about the other two: very unlikely I'd say due to the GROSS HERESIES they spout off as truths yet being diametrically opposed to God, as mentioned in the preamble, and embrace everything He describes as ABOMINATIONS, their cults amounting to SPIRITUAL PROSTITUTION as they'd know if they actually represented God.
As you can see, although it may be true that only Baptists fulfil the requirements for reaching Heaven, anyone actually doing so actually would.