Deuteronomy 25:9

Loose his shoe — As a sign of his resignation of all his right to the woman, and to her husband's inheritance: for as the shoe was a sign of one's power and right, Psalms 60:8, Psalms 108:9, so the parting with the shoe was a token of the alienation of such right; and as a note of infamy, to signify that by this disingenuous action he was unworthy to be amongst free — men, and fit to be reduced to the condition of the meanest servants, who used to go barefoot, Isaiah 20:2, Isaiah 20:4.