What does the human body analogy teach in 1 Corinthians 12:12?

Les explains that in 1 Corinthians chapter 12, verse 12, Paul uses the human body as an example. For as the body is one and has many members, and all the members of that one body, being many, are still one body. Paul is talking about this body: we have eyes, hands, fingers in their purpose, and they are singular in their nerve endings. If you strike your thumb with a hammer, the whole body hurts, not just the thumb, and it all goes to the central nervous system. Paul uses that as an example, and then says at the end of the verse, “So also is Christ.” He is the head of the body, which is composed of many members. Les notes that some ridicule the idea of the so-called body of Christ as an invisible entity, but the Scripture does not; it teaches it, especially in Paul’s writing, that we now become members of the body of Christ, of which He is the head in heaven, and we are the body still here on the earth. How did we become a member of the body of Christ? You did not sign up for it. Some preacher did not baptize you into it, but first you had to believe the gospel, and the Holy Spirit automatically, immediately, the moment we believe, verse 13, for by one Spirit.