Our feet without socks cling and hold on to a lot of the clutter that lies within the house. Then in that day, dust was prominent considering the territory of lands traveled. Jesus told his disciples to kick off the dust of their feet when one doesn’t listen to their message they came to preach, which was a message to the Jewish nation first as the main focus and concern. Jesus, exclaimed since he washed their feet, so also they too.
Why was it that Jesus washed His apostles’ feet, but when Peter suggested that He wash more than his feet, Jesus then answered?
"... He that is washed needeth not save to wash his feet, but is clean every whit: and ye are clean, but not all." John 13:10
The purposes of the heart and head of each, except Judas Iscariot, were clean.
“For he knew who should betray him; therefore said he, Ye are not all clean.” John 13:11
All of them had walked in places that were unclean. That is to say, they had each and every one of them walked in sin. Jesus was preparing them to walk on a new pathway. Only the one mentioned retained evil purposes in his heart and he alone needed more than a foot washing.
“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
How can we walk along the “highway of holiness” [Isa 35:8] when our feet are still unclean from the sinful pathways on which we have already walked?
Thus it was needful for the priests under the old covenant to wash themselves so as not to defile the tabernacle in the wilderness or the temple. This was a shadow of the place where we are to enter with Jesus and His Father.
"So they shall wash their hands and their feet, that they die not: and it shall be a statute for ever to them, even to him and to his seed throughout their generations." Exo 30:21
Jesus explains here why it was not necessary to wash one’s hands:
“But those things which proceed out of the mouth come forth from the heart; and they defile the man.
For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies:
These are the things which defile a man: but to eat with unwashen hands defileth not a man.” Matt 15:18-20
"The LORD maketh poor, and maketh rich: he bringeth low, and lifteth up.
He raiseth up the poor out of the dust, and lifteth up the beggar from the dunghill, to set them among princes, and to make them inherit the throne of glory: for the pillars of the earth are the Lord's, and he hath set the world upon them.
He will keep the feet of his saints, and the wicked shall be silent in darkness; for by strength shall no man prevail.” I Sam 2:7-9
"And she arose, and bowed herself on her face to the earth, and said, Behold, let thine handmaid be a servant to wash the feet of the servants of my lord." I Sam 25:41
"God is my strength and power: And he maketh my way perfect.
He maketh my feet like hinds' feet: and setteth me upon my high places." II Sam 22:33-34 [Ps 18:33][Hab 3:19]
"He brought me up also out of an horrible pit, out of the miry clay, and set my feet upon a rock, and established my goings.” Ps 40:2
“For thou hast delivered my soul from death: wilt not thou deliver my feet from falling, that I may walk before God in the light of the living?” Ps 56:13
“The righteous shall rejoice when he seeth the vengeance: he shall wash his feet in the blood of the wicked.” Ps 58:10
“I thought on my ways, and turned my feet unto thy testimonies.” Ps 119:59