As many of you know, I once wrote an article titled He was buried, in order to demonstrate why belief in the immortality of the soul means someone can’t be said to be a member of the body of Christ, since it would mean one doesn’t believe a specific (and crucial) element of Paul’s Gospel (please go read that article if you aren’t familiar with why I say this).
I’ve also maintained for years that the “Christ died for our sins” element of Paul’s Gospel means that someone who believes in Infernalism (meaning the doctrine of never-ending torment), or even Annihilationism, can’t actually be a member of the body of Christ, because they don’t believe that sin has been dealt with, once and for all, through Christ’s death for our sins (if anyone believes that a person can be punished without end because of their sins, they haven’t understood what it means that “Christ died for our sins,” and you can’t truly believe something if you don’t actually understand its meaning). Not only that, though, it also means that someone who believes a person can only be saved by choosing to believe something specific aren’t in the body of Christ either, because it isn’t our belief that saves us, but rather it’s Christ’s death for our sins, along with His subsequent burial and resurrection on the third day, that saves us (this means that even some who call themselves “Christian Universalists” aren’t in the body of Christ, because many of them also believe that salvation only comes through a choice to believe something specific). To believe that one has to choose to believe something specific in order to be saved is putting the cart before the horse, since faith, or belief, in what Christ accomplished is the cart bringing us into the form of salvation known as membership in the body of Christ (also known as salvation from a relative perspective), while salvation (from an absolute perspective) because of Christ’s death for our sins, burial, and resurrection on the third day, is the horse.
I should say, while “the salvation of all humanity” isn’t, strictly speaking, Paul’s Gospel itself — since Paul’s Gospel is technically just those combined elements that he said he taught the Corinthians (Christ’s death for our sins, His burial, and His resurrection on the third day) — because the salvation of all humanity is the end result of Christ’s death for our sins, His burial, and His resurrection on the third day, it means that the salvation of all humanity because of what Christ accomplished is this Gospel’s main point. And so, while there are other details about his Gospel which also need to be understood in order to be considered a member of the body of Christ, it can legitimately be said that “the salvation of all humanity because of what Christ accomplished” is essentially Paul’s Gospel.
Despite all this, it’s been stated by many people that 1 Corinthians 15:1-4 was talking only about those in the Corinthian church who believed Paul’s Gospel (or at least only about people who believed Paul’s Gospel in general), and that it didn’t include the rest of humanity anywhere in its words, and, in fact, that the “for our sins” part of this Gospel was only referring to the sins of the Corinthians who believed that the words in Paul’s Gospel are true (or at least only referring to the sins of those who believe his Gospel in general). And while it is true that this part of the chapter was about what the Corinthians specifically believed (and it’s also true that what Paul wrote in this chapter about his Gospel includes a reference to a form of salvation that not everyone will experience, since those he brought the Gospel to weren’t saved if they have believed in vain), what they specifically believed wouldn’t actually make any sense if “our sins” wasn’t referring to the sins of all humanity.
I mean, aside from the fact that he didn’t tell them something along the lines of, “Christ can have died for the sins of you Corinthians specifically, but only if you happen to believe that He died for your sins, making it so that He did die for your sins, even though He didn’t actually die for your sins if you don’t believe He did” (which would have to be the case if this passage was only about the sins of the Corinthian believers rather than the sins of all humanity), why would he have called this the good news he brought to them if it wasn’t already news which is good for his audience at the time he spoke it to them in person, before they even believed it? (This is why it’s called good news/a Gospel to begin with: because it’s good news whether someone believes it or not, or even hears it or not — it couldn’t be called good news if it’s something that has to be believed in order to avoid a never-ending punishment, since it could then only be called potential good news, or Paul’s Potential Gospel.) The statement that “Christ died for our sins” would have to already be good news to anyone Paul told this fact to before he even spoke the words to them if he wanted to be able to call it a Gospel in the first place, and not just news which can be good, but only if they happened to hear it and then also believe it’s true, somehow turning it into good news for them (although not really particularly good news, since, statistically speaking, they were still pretty much guaranteed to lose most of their loved ones to never-ending punishment in the end, especially if modern Christians are correct).
I should also say, this is where the Calvinists are at least partly correct (or at least those Calvinists who don’t say unscriptural and illogical things such as, “Christ’s death for our sins was sufficient to save all, but efficient to save only the elect,” because if something must be added to His sacrifice in order for someone to be saved — even something as simple as having to believe the right thing — then His death for our sins was, by definition, INsufficient on its own to save anyone). The consistent Calvinists at least understand that, if we can’t do anything at all to save ourselves, it can only be Christ’s death for our sins (along with His subsequent burial and resurrection) that saves us, which means that anyone whose sins Christ died for has to be saved, since otherwise His death for our sins accomplished absolutely nothing for anyone prior to someone hearing about His death for our sins and then choosing to believe that His death for our sins accomplished something for them too, thus making them their own (at least partial) saviour by turning Christ’s ineffectual action (which, by definition, is what His death for our sins would be if it didn’t have any effect without someone else doing something, such as choosing to believe something specific, to add to it as well) into an action that finally helped accomplish something for them after all.
Where these Calvinists go wrong is in forgetting that the words Paul specifically said he spoke to the Corinthians when he first evangelized to them in person were not “Christ died for your sins” (or even “Christ died for the sins of the elect,” which is what most Calvinists believe he meant). Instead, he wrote that the words he told them in person were “Christ died for our sins.” If he only meant that Christ died for the sins of the Corinthians and himself specifically, it would mean He didn’t also die for the sins of anyone else, including the believers in Rome or Galatia or anywhere else for that matter (and that He didn’t die for your sins either). But let’s say that he just meant “the sins of the elect,” or even “the sins of believers in general” (to make this point clear to those who aren’t Calvinists as well), when he said “our sins.” Well, since it’s not like believing Christ died for our sins could then make it a fact that he died for their sins specifically, but only after believing it (since He only died once), this means He had to have at least died for the sins of anyone hearing this proclamation of good news before Paul spoke those words to anyone. And so, unless every single Corinthian Paul spoke to believed his words, if Christ’s death for our sins is what saves us, it would mean that Paul was lying to anyone who didn’t believe that Christ died for our sins when he spoke those words to them, because that statement would have to include everyone hearing him say those words rather than just the listeners who also believed those words were true (since it would mean that Christ didn’t actually die for their sins after all, considering the fact that anyone whose sins Christ died for has to be saved). Not only that, it would mean we were also lying anytime we explained that the good news includes the fact that Christ died for our sins, at least if anyone who heard us didn’t believe it either (unless, perhaps, what one actually has to believe in order to be saved is that Jesus died only for the sins of Paul and the Corinthians he spoke to — and that everyone in Corinth he preached his Gospel to got saved — and not that he actually died for you or anyone else, but then we’d have to ask what the basis of our salvation really was in the first place).
So yes, Christ’s death for our sins actually had to apply to all humanity, and if someone doesn’t understand that this means everyone has been saved from an absolute perspective, they can’t be said to be in the body of Christ yet.
That said, there’s more to know about joining the body of Christ than just understanding that Christ’s death for our sins saved everyone, so if you’d like to learn more, please check out this in-depth study on the topic: What the Bible really says about heaven, hell, judgement, death, and salvation