Dust

Jesus in answer to Peter's objection to a foot washing said, "If I wash thee not, thou hast no part with me." Peter then wants to be fully washed, but Jesus explains that he has already been washed (a reference to baptism), and that a person who has already bathed needs only to clean the dust from their feet. We are the redeemed, dust represents point of contact with the temporal world. We are in the world, but not of the world. Genesis 3:19 "for dust thou art, and unto dust thou shalt return." Dust is the stuff we're made from, it speaks of the created material world. We have this treasure in earthen vessels.