Romans 12:4-5 — For as we have many members in one body, but all the members do not have the same function, so we, being many, are one body in Christ, and individually members of one another.
Paul is talking about unity and harmony — and diversity
function (office) — not a position but a function. The same word is translated "deeds" in Romans 8:13.
We are a common body because of our unity in Christ.
1 Corinthians 12:12 — 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.