He it is, who coming after me is preferred before me, whose shoe's latchet I am not worthy to unloose. John 1:27
"John’s humility comes to expression again when he says that he is not worthy to untie the lachet of Christ’s sandal. This takes us back into the travel on the hot and dusty paths of Palestine. As one walked in the heat and the dust, one’s feet inevitably become dirty. When one came into a friend’s house, the first courtesy provided was water to wash the guest’s feet. But the host would not normally do this himself. To attend to the feet was a task fit for a slave, and it would be a slave who was expected to do the actual washing of the feet.
We may get a little help in appreciating the significance of John’s words if we reflect on customs among students and rabbis. Rabbis were not paid for teaching their disciples. Their teaching was always in one way or another instruction in the Bible, and they held that it would be a dreadful thing to take money for teaching God’s Word. So a rabbi’s needs had to be met in some other way. It was the custom for every Jewish boy to learn a trade. Sometimes we are told that this arose out of some grand notion of the dignity of labor: I greatly doubt this. In the case of people like rabbis it was sheer economic necessity. If the rabbi could not be paid for teaching, it was obviously important that he get a little money in some other way (cf. Paul and his tentmaking [Acts 18:3]).
But that was not the whole story. The rabbi could not work a full day and still have time to devote to his studies. Here the students could help. They were expected to perform all manner of little duties that freed their rabbi from preoccupation with the minor chores of life and gave him time to put into his books. There is a pertinent regulation which in its present form is dated about A.D. 250 but is probably much older. In view of John’s words it is not unlikely that it went back to New Testament times.
It reads: "Every service which a slave performs for his master shall a disciple do for his teacher, except the loosing of his sandal lachet." The feet of even godly and learned rabbis got hot and dusty and smelly. It would be most unpleasant to perform the office of taking off the sandals and washing those feet. It was just too much to expect of a student. Anything else he would do. Cheerfully. But, please, not the sandal lachet! It is fascinating that John selects precisely this duty which the student would not do for his rabbi and says of it, "I am not worthy."
(Morris, Leon. 2000. Reflections on the Gospel of John. Peabody, MA: Hendrickson Publishers., pgs 33-34)