There was the fact of washing the feet of the disciples by Jesus. What does it mean ?
Jesus explained this himself to his disciples:
When he had finished washing their feet, he put on his clothes and returned to his place. “Do you understand what I have done for you?” he asked them. “You call me ‘Teacher’ and ‘Lord,’ and rightly so, for that is what I am. Now that I, your Lord and Teacher, have washed your feet, you also should wash one another’s feet. I have set you an example that you should do as I have done for you. Very truly I tell you, no servant is greater than his master, nor is a messenger greater than the one who sent him. Now that you know these things, you will be blessed if you do them.
John 13:12-17, New International Version
The disciples were to hold themselves as servants of one another. Similarly, all Christians should do the same.