Mark 10:42 (ESV) And Jesus called them to him and said to them, “You know that those who are considered rulers of the Gentiles lord it over them, and their great ones exercise authority over them. 43 But it shall not be so among you. Whoever would be great among you must be your servant, 44 and whoever would be first among you must be slave of all. 45 For even the Son of Man came not to be served but to serve, and to give his life as a ransom for many. (see also Matthew 20:26, 23:11, Mark 9:35)
Jesus' disciples were arguing over who was going to be granted the most prestigious place in the Kingdom of God. In reply, Jesus turns conventional values on their head. "The first will be last, and the last will be first (Matthew 19:30, 20:16, Mark 10:31, Luke 13:30)." Whoever want to lead must serve (Matthew 23:11, Mark 10:44). Such radical teaching is very likely the only lasting remedy to the all-too-common principle: "power corrupts."
John 13:3 (NIV) Jesus, knowing that the Father had given all things into his hands, and that he had come from God and was going back to God, 4 rose from supper. He laid aside his outer garments, and taking a towel, tied it around his waist. 5 Then he poured water into a basin and began to wash the disciples' feet and to wipe them with the towel that was wrapped around him...12 When he had washed their feet and put on his outer garments and resumed his place, he said to them, “Do you understand what I have done to you? 13 You call me Teacher and Lord, and you are 
right, for so I am. 14 If I then, your Lord and Teacher, have washed your feet, you also ought to wash one another's feet. 15 For I have given you an example, that you also should do just as I have done to you."