In the scripture reading for this message, Jesus tells us that greatness in the kingdom of God is the exact opposite of greatness in the world. In the world, great people have many people under them... the more the better. In the kingdom of God, a great person serves others and the greatest person is the slave of all.
This does not mean that the greatest in the kingdom obey others. It means that great people in the kingdom are looking out for others. Love is the central force in the kingdom of God.
So how do we become the servant of all... not just the nice people, but the people who make it difficult to be kind to them?
First, remember what Christ has done for you. You are redeemed, adopted, reconciled, chosen, restored, renewed, cleansed, etc. You are right with God becuase of what Jesus has done. Unfathomable love has been shown to you. Loved people love people.
Second, remember who is important to Christ. Not just you, but the whole world... including those people who can be difficult to love and serve.
Third, remember that in the end, every situation is between you and God. The other people -- the difficult people -- are just "the current situation." How you treat other people -- whether you serve them or not -- is not between you and them. It is between you and God. It is always between you and God.