The Church is Christ’s Body. Yes, this image is a metaphor, and so we must be careful of literalizing the image beyond what the metaphor carries.
That said, a human body is not just the aggregate sum of its parts. You don’t just pile a bunch of organs and limbs on a table and say: There’s a human body. No, that’s a collection of human body parts. Similarly, you don’t just stitch body parts together in any old way that you want. For a human body to be human, it’s organs and limbs will be arranged in ways that are, well, human. There won’t be a foot sticking out of the middle of the forehead and there won’t be an arm sticking out where the leg should go. A human body is organized, quite literally: it’s organs (and limbs) are arranged in a definite shape, order and extension.
Now, let’s turn to Scripture, and I’ll say a bit more about this metaphor.
For as the body is one and has many members, but all the members of that one body, being many, are one body, so also is Christ. For by one Spirit we were all baptized into one bodywhether Jews or Greeks, whether slaves or freeand have all been made to drink into one Spirit. For in fact the body is not one member but many. . . .
But now God has set the members, each one of them, in the body just as He pleased. . . .
But now indeed there are many members, yet one body. . . . But God composed the body, having given greater honor to that part which lacks it, that there should be no schism in the body, but that the members should have the same care for one another. And if one member suffers, all the members suffer with it; or if one member is honored, all the members rejoice with it.
Now you are the body of Christ, and members individually. And God has appointed these in the church: first apostles, second prophets, third teachers, after that miracles, then gifts of healings, helps, administrations, varieties of tongues. (1 Corinthians 12:12-14, 18, 20, 24-29, NKJV)
Now, note that what I have described above, on the basis of the human body metaphor–it’s ordered arrangement, it’s greater-than-the-sum-of-the-parts, and so on, are precisely the very things St. Paul says about the Church with regard to the metaphor.
Now, here’s the thing: Christ’s Body existed on the Day of Pentecost and looked a certain way, was arranged and ordered a certain way. That Body continues to exist, because it is Christ’s Body and he promised to keep it, and it continues to look a certain way, is arranged a certain way and is ordered a certain way. No limbs have been lopped off. No organs have been cut out. No parts have been rearranged. Muscles have developed and gotten stronger. Ligaments and tendons (cf. Eph 4:16) have grown stronger and more resilient as the Body has grown and increased and developed (just like all human bodies do). But it is the same essential body.
Now, many today, including the churches in which I was raised, want to claim to be the New Testament Church. But look around. The matter of identification isn’t hard. Do they look the same? Are they shaped and arranged the same way? Do they have bishops (Acts 20, 1 Tim 3 and 5)? Do they observe a Lord’s Supper which is the very real participation in the Body and Blood of the Lord in the bread and the wine (1 Corinthians 10-11)? Do they hold to the traditions handed down from the Apostles (1 Thessalonians 2)? If they don’t look like, act like, have the same dimensions and arrangements that the New Testament Body had, how can they be the New Testament Body?
Now, granted, the New Testament Church today looks a little different than it did in the first century: after all, I, as a near-forty-year-old man look different than when I did as a teenager. But people who haven’t seen me in years still recognize me, because I still look pretty much the same, still act pretty much the same. So, too, the differences in the New Testament Body of Christ today and that of the New Testament Body in the first century, are differences of growth and development of a body, an organism.
On that basis, it’s pretty easy to figure out where and who is the Body of Christ.