What does Paul use the human body as an example of in 1 Corinthians 12:12?
Paul uses the human body as an illustration of Christ and His body. As one physical body has many members yet remains one body, so Christ is head of a body composed of many members—believers placed into it by the Holy Spirit when they believe the gospel.
Les explains that 1 Corinthians 12:12 follows the same concept, with Paul using the human body as an example. The human body is one yet has many members, and all those members, though many, are still one body. He illustrates this with eyes, hands, and fingers, noting their singular nerve endings: if you strike your thumb with a hammer, the whole body hurts, because everything goes to the central nervous system. Paul then applies this: 'So also is Christ.' Christ is the head of the body, which is composed of many members. Scripture teaches that believers become members of the body of Christ, with Him as head in heaven and they as the body on earth. This membership does not come by signing up or by a preacher baptizing someone into it; it comes by believing the gospel, and the Holy Spirit places them in immediately when they believe, by one Spirit.
For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ.