Joh 13:1  "Now before the Feast of the Passover, when Jesus knew that his hour had come to depart out of this world to the Father, having loved his own who were in the world, he loved them to the end." 

Jesus was the Passover Lamb, the sacrifice for the people of God. The Passover feast was approaching, those who accepted the sacrifice of The Lamb and were obedient to The Father, would be passed over when the judgment of eternal death was issued. God the three in One is Absolute Love, Jesus of Nazareth is Yahweh, the everlasting One. He loves those in the World who are His own-they belong to Him-He loses none of them-He loves them to completion-they are united into Him- with the Father-by the Spirit.

He was sharing the Seder meal with His closest followers.

http://www.chabad.org/holidays/passover/pesach_cdo/aid/1998/jewish/The-Seder-Plate.htm

God had already allowed Satan to put betrayal and deception into the heart of Judas. 

The Seder was filled with gladness and bitterness. Redemption and judgment. 

Jesus knew The Father had left everything in His hands. He would accomplish the will of God and return to the Fathers' side triumphant. 
He rose up took the posture of a servant. Washing the feet of those who relied upon Him for their every breath. He wiped away all the dirt and cleansed them from the dusty filth they had accumulated during their life journey. 

Joh 13:2 - 5  "During supper, when the devil had already put it into the heart of Judas Iscariot, Simon's son, to betray him, 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, rose from supper. He laid aside his outer garments, and taking a towel, tied it around his waist. 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." 

Peter's human pride held Him back from fully receiving the gifts Jesus offered. It is difficult for us to admit need and humbly receive. Peter said; "You shall never wash my feet!"
Jesus said; "You cannot be a part of My kingdom unless you allow Me to cleanse you."

Joh 13:6 - 8  "He came to Simon Peter, who said to him, "Lord, do you wash my feet? Jesus answered him, "What I am doing you do not understand now, but afterward you will understand.  Peter said to him, "You shall never wash my feet." Jesus answered him, "If I do not wash you, you have no share with me." 

Peter still didn't get it. He said; "Then I want you to wash me all over my body." It was spiritual cleansing that Jesus referenced. 
Jesus said; "The people who I have bathed with My Spirit, only needs to keep clean from the dirt gathered from walking in this world, inside that person is completely washed and clean." "You are clean but not everyone."

Joh 13:9, 10  "Simon Peter said to him, "Lord, not my feet only but also my hands and my head! Jesus said to him, "The one who has bathed does not need to wash, except for his feet, but is completely clean. And you are clean, but not every one of you." 

Jesus knew who belonged to Him and who didn't. So He knew Judas was going to betray Him. It wasn't a surprise, it was part of the plan. God uses even the evil of hearts turned to Satan's devices to accomplish His purposes. 

Joh 13:11  "For he knew who was to betray him; that was why he said, "Not all of you are clean." 

He finished His point demonstrated in washing the feet of His followers. He wanted to be clear."I want you to imitate My actions and My attitudes, I Am a servant and I want you to serve and have the heart of a servant." "You follow Me by serving one another;" Jesus told them. 

Joh 13:12 - 15 "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? You call me Teacher and Lord, and you are right, for so I am. If I then, your Lord and Teacher, have washed your feet, you also ought to wash one another's feet. For I have given you an example, that you also should do just as I have done to you." 

Jesus went on; "This is something I don't want you to miss." "You need to follow by doing the same things I do, and having My heart for others around you." "You will find happiness in giving up yourself for others." 

Joh 13:16, 17  "Truly, truly, I say to you, a servant is not greater than his master, nor is a messenger greater than the one who sent him. If you know these things, blessed are you if you do them." 

Jesus knew who were the chosen followers, they were the ones His message was for.
He wanted them to know everything that would happen, even though they wouldn't understand what it meant until it took place. He wanted them to see how all that He did and would do completed scriptural prophecies. He wanted them to have a complete understanding to build their faith upon. He wanted them to be sure that He was Yahweh, that He was completing the works of God. 

Joh 13:18, 19  "I am not speaking of all of you; I know whom I have chosen. But the Scripture will be fulfilled, 'He who ate my bread has lifted his heel against me.  I am telling you this now, before it takes place, that when it does take place you may believe that I am he."