You can easily enough see how this kind of thing works by looking no further than your own body. Your body has many parts - limbs, organs, cells - but no matter how many parts you can name, you're still one body. It's exactly the same with Christ.
By means of his one Spirit, we all said good-bye to our partial and piecemeal lives. We each used to independently call our own shots, but then we entered into a large and integrated life in which he has the final say in everything. (This is what we proclaimed in word and action when we were baptized.) Each of us is now a part of his resurrection body, refreshed and sustained at one fountain - his Spirit - where we all come to drink. The old labels we once used to identify ourselves - labels like Jew or Greek, slave or free - are no longer useful. We need something larger, more comprehensive.
I want you to think about how all this makes you more significant, not less. A body isn't just a single part blown up into something huge. It's all the different-but-similar parts arranged and functioning together.
If Foot said, "I'm not elegant like Hand, embellished with rings; I guess I don't belong to this body," would that make it so?
If Ear said, "I'm not beautiful like Eye, limpid and expressive; I don't deserve a place on the head," would you want to remove it from the body?
If the body was all eye, how could it hear? If all ear, how could it smell?
As it is, we see that God has carefully placed each part of the body right where he wanted it.