For all whom the Son of God gave His life for, have been grafted into His body. His physical body? Not really so. But His body here refers to the church (Matt. 16:18); we, being the body and Christ being the head of the church, His church.
This has a universal tone to it, but we see in the Bible that it unfolds into smaller units, commonly known as 'the local church'; where the church universal is not geographically bound, but local churches are.
We discuss the necessity of the saints and their belonging to a local church as a sign of belonging to the church universal and the scriptural forms of a local church.