Paul's body metaphor does real theological work: it makes the church constitutive rather than optional — you cannot be a Christian alone, because a hand is not a hand off the arm. It also flattens hierarchy in one direction and complicates it in another: no member may be dispensed with, but members differ in function, and the passage that says so is the same one that lists apostles, prophets, and teachers in order. Denominations that emphasize the visible institutional church and those that emphasize the invisible fellowship of believers both cite it.