Well, I guess we all can say, "We blew that request!" "...keep yourselves united..." is far from reality today. But Paul wanted the believers to be united because that would allow the Body of Christ to function more effectively! It would also help fulfill Christ's commandment that we love one another. Remember what He said back in John 13:35, "Your love for one another will prove to the world that you are My disciples." If we are going to truly serve our Savior then we need to serve Him as one body.
It is important to remember that Paul taught that we have diverse talents and abilities. Like our different body parts have different functions, they all work together for the benefit of the whole. Paul wanted us to realize that our diversity was not to offend each other but to compliment each other.
If we are going to live lives worthy of our calling then let us do so as one Body and seek to learn how we can best use our gifts to strengthen the Body of Christ.