On the night before the Passover, Jesus, though He was their Lord took the role of a servant and washed His disciples' feet.
He did this to show that He did not come to be served, but He came to serve by washing us of our sin so that we might share in who He is.
His love for those He came to save and the knowledge that He was the Heir of the Father who loved Him compelled Him to live as a Servant.
Those who have faith in Christ share in His identity as both an heir and a servant.
Since the Father has given all things to Christ as an inheritance, and since we share in Christ's identity as an heir, instead of using others as a way of grasping at getting the most out of life, treating them as our servants, we can empty ourselves in glad service to others, knowing that all we'd ever need for our joy is already ours because Christ served us.