Deuteronomy 6:8

8. Thou shalt bind them… upon thine hand, and… between thine eyes The Jews applied this literally. The so-called phylacteries, in Hebrew tephillin, are leather boxes with four compartments, in which are put four portions of the law written on parchment. The passage is Exodus 13:9. On this box is the letter שׁ , (shin,) written in the usual form, for the right hand side of the wearer, and the same letter with four strokes for the left hand side. There was another box with only one compartment, but with the same passages for the arm of the worshipper. The phylacteries were bound to the forehead and arm by long leather straps. The straps around the head were to be tied in the shape of a ד , (daleth.) The straps on the arm must go around it seven times, and three times around the middle finger, with enough over to form the letter י , (yodh.) Thus, by the shin on the leather box, the daleth on the forehead, and the yodh on the hand, would be formed the word Shaddai the Almighty.