What the Bible says
“Having loved his own which were in the world, he loved them unto the end.”
John 13:1 (KJV)
“For he knew who should betray him; therefore said he, Ye are not all clean.”
John 13:11 (KJV)
“If I then, your Lord and Master, have washed your feet; ye also ought to wash one another's feet. For I have given you an example, that ye should do as I have done to you.”
John 13:14–15 (KJV)
He knew, and he knelt anyway
Washing feet was the work of the lowest servant. On the night before his death Jesus took a towel and a basin and went from disciple to disciple. John makes sure we understand that Jesus was not caught off guard: he knew who would betray him. Judas's feet were washed by the same hands as Peter's and John's.
Love that does not wait to be deserved
Scripture says God commends his love toward us in that, while we were yet sinners, Christ died for us (Romans 5:8). The foot-washing is that truth in miniature. Jesus did not serve Judas because Judas had earned it. He served him because that is who Jesus is. It was also one last open door — an act of tenderness offered to a man who could still have turned back.
The example he left us
Jesus said plainly that this was an example. Most of us are not asked to serve someone who is about to betray us, but we are asked to serve people who have hurt us, disappointed us, or do not deserve it. Humble love, offered first, is the mark of his followers.
Common questions
Did Jesus know Judas would betray him when he washed his feet?
Yes. John 13:11 says he knew who should betray him, and in John 13:18 he quotes Psalm 41:9 about the friend who ate his bread and lifted up his heel against him.
Why did Jesus wash the disciples' feet?
To show the humble, serving love he expected of them. He called it an example: they were to wash one another's feet (John 13:14–15).