Did Paul already know about the Body of Christ when he wrote 1 Corinthians?
Yes. Paul already had knowledge of the Body of Christ when he wrote 1 Corinthians, since he introduces and describes it in that letter. Although the doctrine reaches its fullest expression in his later present epistles, it does not mean Paul knew nothing of it earlier.
Les teaches that even though the Body of Christ as a doctrine is brought to its fullest forte in the present epistles, it does not mean Paul knew nothing of it, because here in 1 Corinthians he introduces it. Les explains that here we have the description of the Body of Christ. He notes that many people do not understand this concept, that every true believer is a member of the Body of Christ. He also points out that Jesus never once mentioned the Body of Christ.
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.