Seeking a hand or foot in the Body of Christ

I've been thinking -- if the Church is the Body of Christ and we are all called to serve different functions, would it not follow that there are different times in our lives when we need different parts? For example, perhaps we need a hand at one point in our lives and later the hand has served its purpose and now we need a foot?

I wonder why it is that we believe our individual churches have to function as all parts of the body. Or maybe it's just mainline established denominations and the people in them that tend to think this way? What if joining a church when one is baptized and remaining in it until death is just not the way it is supposed to work?