The Church is (in) Christ!
It exists in Christ and is part of Christ, just as the body is part of the whole; the person. The body is connected to the head, and the head to the body. They make up the person.
The one needs the other. The Lord Jesus Christ needs His body to express Himself on this earth. He is limited unless we allow ourselves to be built together to form His body.
Let yourself be built together, like living stones built around the cornerstone, to form His spiritual house, so that He may have a home and a body through which He can express Himself!
1 Peter 2:4-9