The Jews were commanded to write the divine name on the posts (mezuzoth') of their doors (Deut. 6:9). The Jews, misunderstanding this injunction, adopted the custom of writing on a slip of parchment these verses (Deut. 6:4-9, and 11:13-21), which they enclosed in a reed or cylinder and fixed on the right-hand door-post of every room in the house.
Easton's Bible Dictionary. M.G. Easton. 1897.