‘For even as we have many members in one body, and all the members have not the same office, so we, who are many, are one body in Christ, and severally members one of another.'
There is a clear resemblance between this description of God's people as a body, and the description of it as the olive tree (Romans 11:16-24), the similarity lying in the fact that they are one whole, and yet separate members of one whole. We may see a difference lying in the fact that the olive tree had had included in it the branches of rejected Israel which had been broken off, but the same may be said of the body (John 15:1-6). In neither case is what has been broken off a genuine constituent of the true olive tree and the true body. The other difference is that the olive tree had indicated ideal Israel in its association with the promises of God and with the Messiah. This indicates the living body in which His people are united as one in Christ (Galatians 3:28), in the body which IS Christ (1 Corinthians 12:12), in what is the new nation of Matthew 21:43, in the new Vine of John 15:1-6. Note that the body is never seen as distinct from Christ, for the body is Christ's body into which the members have been incorporated. It is Christ Himself Who is the body. It is therefore wrong to speak of the church as ‘the body of Christ on earth'. Rather the church has been united with Him in His heavenly body, and is in the heavenlies in Him (Ephesians 2:1-6), while physically operating on earth.
But the consequence of this is that His body has many members, each having his part to play in building up the whole. Each does not have the same office, for differing gifts have been distributed to some throughout the body. But all are to remember that they are one body in Him, and must therefore maintain unity, being members one of another (see 1 Corinthians 12:12-27).