One verse in the New Testament defines the "body of Christ." 1 Corinthians 12:27, "Now ye are the body of Christ, and members in particular." Paul says that the church at Corinth is the body of Christ. He says, "Ye," not "we." Paul was a believer, so by excluding himself, he surely defined the body of Christ as the assembly, the congregation, only local. If the body of Christ is all believers, then every saved person in the world was in Corinth. We know that isn't the case.
Let me deal with a couple of arguments brought against this understanding of 1 Corinthians 12:27. It probably seems pretty cut and dry to you. "Ye are the body of Christ," speaking to a church in a particular locale, then the body of Christ must be a congregation of believers. Well, men have developed their beliefs to include what they call a "universal, invisible church." Invisible church gives me a little chuckle. If you ever visit our church, and think there aren't enough people, well, you should just understand that you only see the visible church, not the invisible. H. G. Wells would be proud. They all have their Tolkien rings on and this renders them, yes, invisible. OK, enough chuckles. There isn't a universal church. Those two terms are mutually exclusive. Anything that congregates or assembles is not universal. Air is universal. We could say universal water. Universal wind. Universal space. But not universal church.
The first argument I get is this. By the way, many men blush when they give these arguments because they seem so lame. But here it is: The church at Corinth is the body of Christ, but there is also the universal body, the mystical one, so there are actually two bodies of Christ. It would go like this: You at Corinth are the body of Christ and then all believers are also the body of Christ. Ephesians 4:4 should ruin this argument, when it says, "There is one body." Ouch!!! Well, we do know for sure there is the body that is the congregation, only local (1 Corinthians 12:27). So if there is only one body, then the big one made up of believers that are dismembered all over the universe must not exist. I've never seen it. Maybe that's why they call it.....invisible.
You say, "Well, that pretty much settles that, doesn't it." No, they keep going after that seemingly clinching Ephesians 4:4 argument. They say, "The one true body is all believers and the local one is a visible manifestation of the one true one." Say again? (Scratching head) It must be convenient to make up new rules for interpretation as we go along. I can't seem to get by with that in any other venue of life. "That was traveling." "No, I just made that rule up, so it was legal!"
This whole "true in the invisible" concept comes from the pagan Greek philosopher Plato. He started the real in the realm of the Idea with physical items just being visible manifestations of them. Why listen to Plato? I don't, but why they do is because Augustine, the Roman Catholic "scholar" liked him. Augustine (pronounced O-gu-stin) lived 354-430 and he became extremely important to the state church in Europe. A group of people who believed the Bible, the Donatists, asked Augustine why so many unconverted were in the Catholic church. Augustine said there was the visible and the invisible Catholic (universal) church. He said that the invisible was the genuine church made up of all true converts and the visible was the one people could see that had some unconverted. The Protestant Reformers were all former Catholics and most of them were big Augustine fans, so they adopted his universal, invisible church idea. It isn't in the Bible.
You ask, "Why is the two body argument wrong?" Because the Bible has only one body (1 Cor. 12:27) and the other isn't in there anywhere. The universal body side will say that certain instances are talking about all believers; they just have to be. The ones they are talking about are when the singular nouns "body" or "church" are used generically, speaking of the "body" or the "church" institutionally. For instance, if I said, "I answered the phone," I wouldn't be talking about a particular phone, but "the phone" as an institution. If I say, "The church is important to God," I'm not talking about a particular church, but the church generic. There is no such thing as a Platonic, Augustinian use of the singular noun. That was made up to protect this doctrine that isn't in the Bible.
The other big argument against 1 Corinthians 12:27 defining the body of Christ as only local is the lack of a definite article before "body" in the Greek text. The English definite article does not translate a definite article in the Greek text behind that English translation. Without that article, universal church or body advocates say that 1 Corinthians 12:27 is saying that the church at Corinth ("ye") is "body material," that the absence of an article makes "body" qualitative---something like: "Ye are the body stuff or material of Christ." They have it all wrong.
The absence of an article does not mean that "body" (soma) is not definite. A. T. Robertson writes in his mammoth Greek Grammar (p. 790), "The word may be either definite or indefinite when the article is absent. The context and the history of the phrase in question must decide." On the next page, A. T. writes under "With Genitives.", "We have seen that the substantive may still be definite if anarthrous (without an article)." Much of the NT koine (common Greek of the NT) is Hebraic. A.T. Robertson writes in his grammar: 'Schaff said that the Greek spoken by the Grecian Jews "assumed a strongly Hebraizing character.' According to Hatch 'the great majority of NT words...express in their biblical use the conceptions of a Semitic race' (p. 88). The genitive construction "body of Christ" fits into this Semitic pattern: the head, "body," the nomen regens; and the tail, "Christ," the nomen rectum.
Compare this with "the angel of the Lord" (angellos Kuriou) in the NT. "Angel," like "body," is treated definite, like a proper noun, so translated "the angel of the Lord," even though no article precedes either "angel" or "Lord." Proper nouns do not need an article to be definite. In John 1:1, the absence of an article with a proper noun does not make "Word" indefinite, i.e., "a god." This is called a Semitism in the New Testament, a word for a Hebrew language influence in the New Testament Greek. For instance, we don’t find the Hebrew definite article in the OT with "the congregation of the Lord," and yet it is called "the congregation of the Lord." This is why they (the KJV translators) translated it "the body of Christ" in 1 Corinthians 12:27.
I believe that uniquely the absence of the definite article occurs here because this is referring to "body" as a proper noun. The proper noun is definite. This makes a stronger argument for "the body" than if it had the article. Soma Christou ("the body of Christ") acts as a proper noun, the official title of God's governing institution in this NT era.
Let's put this in a logical syllogism.
Major Premise: The church at Corinth is the body of Christ.
Minor Premise: The church at Corinth is local only.
Conclusion: Therefore, the body of Christ is local only.
The body of Christ is local only.