For just as each of us has one body with many members, and these members do not all have the same function, so in Christ we, though many, form one body, and each member belongs to all the others.
My body is composed of various parts: hands, feet, eyes, heart, liver, etc. Each of these parts performs a specific function in my body. Some are more essential than others in maintaining life. But all of them contribute to my having a healthy and functioning body. If one part is missing or unhealthy, not doing what it is supposed to, it impacts my whole body.
Paul uses this example of the human body to illustrate the church. The church is composed of many individual members. Each of those members has a role to play in the proper functioning of the church. And the church as a whole is only as healthy as its individual members’ health and proper functioning.
We are generally comfortable in acknowledging that we belong to a church. It simply means that we are a member of it. But Paul goes beyond that in this passage and says we belong to each other. That is much more personal. If you are a disciple of Jesus and a member of his church, then I belong to you, and you belong to me.
Belonging to another implies service. And, as Paul goes on to say, God has gifted us to serve each other. God has gifted me to serve you. And he has gifted you to serve the other body members, including me. The importance of belonging to and serving each other cannot be overstressed. The health of the body and its members depends on each of us faithfully doing our part.